I'd go for a PC. Always. Even though you can use boot camp.
Basically, Apple PCs are overpriced - they mainly get away with it because they look chic and have decent hardware. However, I can build systems from scratch, and I can make superior-specced machines for about half the price of a Mac. I've also noticed that even the newest Macs only come with an 8x DVD burner...
Anyway, as for software, I'd take Windows for the games, and basically because I have 2 more OEM licences. As far as I'm aware, you can't buy Mac OSX to install on a normal x86 machine.
I would occasionally recommend a Mac to a newbie home user though - especially if they have kids - because the kids almost always end up getting a virus or something on Windows. Vista may not be as bad in this respect, but it's not exactly the speediest OS ever. (If you want to refute that, why exactly are there a load of speed fixes in SP1?)
So, in conclusion... build a PC yourself, on the cheap - but still with a great spec, install Windows, and off you go.