get a top of the line Acer or something.
The Acer laptop of a friend of mine was advertised to run Crysis, and it did. A first person shooter from '99 had trouble though...
It went a lot
better since we put Windows 7 on it rather than Vista, but I don't trust Acer at all anymore to deliver the specs they advertise. What they advertise is probably true, but somehow all of their laptops are rather slow and break down often (I hear that from just about everyone who owns an Acer or got experience with one).
My current laptop is an Asus EEE 1215n (was €470 about a year ago) and it runs Amnesia on low quality, but not easily. Most other games are also well playable, as long as you put them on low quality. My experience with Asus is that they deliver about the most power for the money. Dell laptops at school are generally more business-focussed and have faster CPUs rather than graphical power, but they game fine as long as you pay enough. One person also got a Sony Vaio which runs fast (about the fastest I've seen), but he never games at all. I suspect Sony also focusses on the business market though, so not that much gaming power. Also it was quite expensive iirc, but I don't remember what the price was.
If you guys can, more specific things like "needs x much ram" and an "x or y or better graphics card in it" are probably more helpful in this case.
RAM: 2GB minimum, but I'd recommend 4.
is a very nice list, I think any CPU above about 1000-1200 score will do. (GHz is not always a good measure.)
GPU: Another good list
, but I'm less familiar with this. I think you need about 700.
For battery life, my EEE-laptop was (iirc) advertised to last 6 hours. If you work normally on it, you get about 5 hours and 30 minutes (or should I say 4 hours and 60 minutes o'harean time here :P). When gaming I estimate about 3 hours, but I'm not someone who plays a game for very long especially on a laptop (we got desktops for gaming, imho), so I never really tried that. So decide what you want it to last under normal load (no games), add about 30 minutes to an hour to that, and tell them that's your requirement for the working time.
I personally am a bit like, as long as it lasts 2 hours I don't care. Within that time there is always a place to plug the power in.
Hmm what else... I'm not sure if you share files between computers somewhere (home, school, ...), but if you do a gigabit ethernet controller would be advisable. Also support for 802.11n wireless would be nice then, the older standard only goes to 54mbit.
Storage and size is something you can probably decide yourself. I think I got about everything now :).
(Note that I might be mistaken on anything though, everything I say is from personal experience, but I'm quite sure it will work out with the above specifications).