Go for an Athlon 64 system. I suggest you get one with the new 90 nm Athlon 64 3500+. It runs cooler than the 130 nm one and uses less power.
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2149&p=7
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2065&p=6
http://techreport.com/ja.zz?comments=7417
I'm buying a new system and found what I wanted. And wanted to know what would be better out of the two since I dont know much about PCI-express yet.
http://www.addictpc.com/index.php?crn=457&rn=2133&action=show_detail
OR
http://www.addictpc.com/index.php?crn=125&rn=2696&action=show_detail

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic