My son needs help purchasing a computer for gaming

[Hallett]

Hi, would appreciate any help I can get, I hate it when my son asks me stuff I don't know, but I had the bright idea of turning to you folks.

We live in Canada, so some of the stores and brands might be different, but basically he is trying to decide whether to just go and buy a Dell, or head to Best Buy, either way buying a brand name off the rack computer, or assemble one himself.

He has done a bit of work, and found this for about $800 CAD, which is about his budget... little bugger wants me to pay taxes for his birthday present:

Processor: Intel core 2 duo E4500 dual core
Motherboard: Intel d946GZIS
Memory: Corsair PC2-5300 2GB
Power Supply: Sparkle Power SPI ATX 400PN @ 400W
Video Card: Geoforce 760GS 400MHZ PCI-E 256MB
Heat Sink: Apparently he does not know if he needs one ??
Hard Drive: Hitachi Deskstar T7K500 250GB Sata2

Apparently this comes with Vista, though he can get Windows XP for another $20.

HELP!!!!