I wouldn't do it. You can get a pretty decent laptop to do a lot of gaming on, but it you want something really powerful they get expensive fast.
I bought an $800 laptop two years ago, and while I wouldn't try to run Battlefield I was able to play Skyrim on it which looked about as good as the 360 version and loaded a hell of a lot faster. The laptop runs anything I want it to. Mostly I just play Source games, but Skyrim, ME2, and Stalker all run fine. Lots of newer games probably aren't so good, so I stay away from them on my laptop.
Even if you spend a lot more than I did, you are probably going to be in my situation in a few years, especially after the next gen comes. That's fine if you just want a laptop that can run TF2, not so much if it's a dedicated gaming rig. Laptops really suffer from diminishing returns. Shop around for the right Asus or something and you can get a pretty decent deal for a grand or so. Spend a lot more than that, and you get something that isn't so portable, is more expensive than a similarly powerful desktop, might get hot, ages quickly, is harder/more expensive to repair should you need to, and is probably more likely to need repairing.