Get an Alienware Laptop and install Windows 7 on it. Alienware offers the best PCs available. My older bro has one, and it's simply awesome.

For a laptop it's rather large, but it will fit into a backpack and it can play the latest games with all the settings at or near the max, no problem.

Here's a link:
http://www.alienware.com/Landings/laptops.aspx