If you're looking for a PC only to game, go for a desktop, otherwise you'll spend the same amount of money for a laptop that's gonna be barely as good as a desktop would be. As others said, screw Alienware, if you have the knowledge, patience and courage to build your own PC, go ahead! Otherwise, there are some good custom PC building websites out there. I suggest you go for Windows 7!
But remember, there's a first to everything, I recently built my first PC, it was a bit of work getting to learn how PCs are made and work and so on, but you'll see, you'll understand PCs so much more if you build it yourself. There are guides on Youtube anyway, I personally followed Newegg's one. Very nice detailed guide divided in 3 parts. Here's the first part :
http://www.youtube.com/watch?v=lPIXAtNGGCwJust make sure you put quite a bit of research if you build it yourself!
Good luck to you, mate!
