I just finished building a new PC with my 12 year old son for his birthday present in August and used the guides at Arstecnica.com to choose the parts (most of them anyway). We chose the Budget Gaming machine to build with an MSI K8N-Neo-F MoBo w/Athlon 64 3000+ CPU. This combination was rated best bang for the bucks and we have been very pleased with it so far. Arstecnica updates their building guides every few months and has a great price searching engine to find the best prices for each piece on the Internet to make it easy to find and buy all the pieces.
My suggestion is to build it yourself if you are capable and want to save some money.
:-D
