The M14 is fine under the "lookalike" rules. In fact, a lot of people use them and they're very good guns, doubling as M1 Garands, German G43 and even Russian SVT's.
As for the P90, it's too "modern" to look even remotely like a WW2 gun, especially with rails and a silencer. However, the P90 gearbox is a great bit of kit for building your own WW2 gun from.
There is a section on the lookalike rules here http://www.ww2airsoft.org.uk/pages/kit-guns.html
When I want your opinion - I'll tell you what it is!
Hello and welcome. Feel free to post something about yourself in the Introduction section. 
WW2 games are run by many different people, and as Sgt Heide has said, if the event in question was using the lookalike system your M14 would be fine - although you would most likely be expected to use it on single shot only. (In fact, I'd also say that ammo limits are one of the most important aspects of most WW2 airsoft games.)
Take a look at the kit guides on the top menu - what kit do you have at the moment? If you're just thinking about giving WW2 airsoft a try, then probably the best way is to borrow kit and a gun.
You've got nothing to ein, zwei, drei, vier
It's not usually up to the sites, Josh. The WW2 airsoft scene (certainly on this forum) is made up of various small groups of organisers (usually non-profit making), who rent out sites around the country to devise, organise and run their games themselves. Therefore, each individual game has its own rules on kit and weapons, usually specified in the game's forum section.
As regards the P90... be honest with yourself - it looks nothing like a WW2 weapon! 
Like I said, you might be surprised at the number of people who will lend you kit when you start.
You've got nothing to ein, zwei, drei, vier
Having looked at the lookalike section, it would appear that I could use the p90 as long as I stick to the rules regarding use of a mp5 in place of a sten etc
No, the P90 is not an acceptable "lookalike" for any weapon. It bears no resemblence to any WW2 weapon (not Korean war, Vietnam war or Falklands war for that matter). Just use the M14, you won't regret it.
When I want your opinion - I'll tell you what it is!
Yup... M14... a few long term players use theirs as M1 Garand's without any modification. They're top guns and highly recommended. A bit later you could convert it to an M1 garand with one of the kits from Shoot n Scoot if you wanted... oh, it does have a wood effect stock doesn't it? That helps quite a bit with it looking right.
P90, forget it. Sorry, but it'd not be allowed at any game I ran for a start.
My opinion should not be given too much significance since I only organize games in Denmark. But in my games we generally accept looks-like weapons as-is if they have the general feel of a ww2 weapon. More specifically the should look like they are made of steel and wood. If this isn't the case we expect the participants to wrap their weapon in small pieces of hessian as if they were trying to conceal it for sniping use. It's not perfect, but it helps a lot. This might be an idea if your M14 has a green or black stock.
A P90 wrapped in hessian will look like a P90 wrapped in hessian. Stick with the M14.
I believe the MP5 counts as an MP40/sten lookalike because it's black and has a convensional 'stick' magazine.
It does indeed. Although, I can't recall ever seeing an MP5 at a game. I think that some of the "lookalikes" rules need reviewing now, in light of the release of weapons such as the Sten and the MP44.
When I want your opinion - I'll tell you what it is!
The look-alike rules are rather legacy now and haven't been used by CiA (or Gunman) for a year or more now but are there for any other organiser to use as a basis for their rules, if they wish.
There will probably always be some degree of compromise for years to come but given the availability of period looking kit now there is less and less need to be so generous in gun types used. But as always its an organiser's call and will be a question of practicality, availability and event style.
A bit of confusion here , the originsal looks alike system was developed for the early CiA games, and the list Heide linked to is a remnant left over as a helpful guide for other would be games orghanisers. Most of the major game organisers, CiA PBi, Army Group South etc have moved onto far stricter rules on weapons.
But as everyone point out your M14 will be more than welcome at most events.
EDIT - chommers beat me to it !
FPS limits are largely site-specific, but bolt-action limits are generally higher than for AEGs and Electric semi-only sniper rifles. There's also been some discussion about dropping them down to within the AEG limits to get rid of the MED (Minimum Engagement Distance) requirement.
Best to go for the "wood" stock VSR10 as a WW2 lookalike. If you're on a budget, it's worth looking at the JG BAR10, a Chinese clone of the VSR10. There's loads of threads about making them look more like an Enfield. A face veil or some hessian wrapped around it helps to disguise the overall appearance.
As for fps, it depends on the site. You don't have to run a rifle at 500fps in order for it to be effective. The BAR10 typically clocks at just over 400fps out of the box. For rifles over 350fps, most sites will have a minimum engagement range (MED) to prevent injury to players and will also insist on you carrying a sidearm for use inside the MED. This will obviously bump your costs up a bit.
When I want your opinion - I'll tell you what it is!
From my local site rules:
AEGs 328fps. (though they allow up to 350 onsite)
Semi automatic sniper rifles is 360FPS.
Bolt Action Snipers 450fpsSnipers must carry back up weapons
On the sidearm point; a WW2-style M1911A1 of covers you for US and British specifically, and others as "private purchase" or "captured".
Thanks for the advice regarding the VSR10 and BAR 10
...
No problem. 
I note you said you would like an M1911A1 as well. Have a look here for a cheap, full metal one http://www.airsoftworld.net/army-detoni ... ter-1.html. Again, it's fully Marui compatible. I have one and it's great.
When I want your opinion - I'll tell you what it is!
I note you said you would like an M1911A1 as well. Have a look here for a cheap, full metal one http://www.airsoftworld.net/army-detoni ... ter-1.html. Again, it's fully Marui compatible. I have one and it's great.
How does it perform in the cold? Would the ABS TM one be better in those circumstances?
I had to get TM mags for it, as the standard one seems to eat gas and only gives me 7 shots! The TM ones both give me a full 24 shots. I've tried it outside in the cold and, using green gas, as long as I don't go mad and stick to double taps, I've had no problems. A plastic framed pistol is usually easier on gas in the winter but hell, the TM 1911 is £140 at most retailers and I'll gladly sacrifice a bit of cold weather performance for the extra "heft" of a full metal handgun, especially when it's almost half the price.
When I want your opinion - I'll tell you what it is!
Yup, have a look on this forum and you'll find a whole thread about using bolt action rifles under 350fps to avoid the MED issue... There are good arguments for both keeping under 350fps and going over 350fps. Read it, make up your own mind. It's not something that should be discussed again on this thread.
BTW, since the M14 is such a long gun and is a rifle anyway, you may be better trading in the P90 for an SMG, for instance a Sten or Thompson. Otherwise you're stuffed for more CQB style skirmishes.
that p90 is just asking to be made into a maxim or vickers gun
or worst case keep it
after starting ww2 the only modern guns i kept were mp5k ,mp5 and an uzi, and the only reason for that was just in case i see a good modern game i may like to do. i sold everything else to fund my ww2 stuff
a thompson is a good all rounder, and can even be used modern day at a pinch
"Take that you rotton helping of strawberry flan!"
Joseph Porta to "strawberrys and cream", in the sven hassel book ,ogpu prison
Im sure there was a photo of Kvaster standing next to a guy in full swat gear with dual mp40's which still looked in keeping with his loadout.
Think we've hit the nail on the head several times here!
if you're after a single action gun, the BAR10 is more reliable from a durability point of view than the MP001. I've just finished making a Mosin Nagant from a BAR10, and my craft skills are same as the next person.
If you wanted to make your M14 look more like a wooden gun, you need only to paint the top heat cover a wood colour, and it'll look fine from any distance.
