The yellow one's build is nice, but for a $500 budget how can you get a $150 dollar mobo. Wait liek 2 weeks until the AMD X2's prices drop so you can ahve an AMD Athlon X2. Here's what i say you get.
AMD Athlon 64 X2 3800
1 gig ram
7600gt
250gig Sata HDD
FSP 450watt psu
Antec super Lanboy Case
MSI Neo4-F mobo
thats agood build that will fit your $500-$700 budget, unless you want to go AM2, then get a cheap AM2 mobo but don't buy that $150 Asus one.