Here's my specs for about or around $600.00. (OS $185) And you don't need Ultimate!

AMD 4800+, Biostar TF7050, 2 gigs mem, 8600gt 256mb,2x WD 120gigs
Lite-On DVDRW LH-20A 1L SATA, Vista Ultimate, Bitdefender IE Security.

I can play Oblivion Maxed out at 1024x768 (monitor only goes that high) Not bad for a cheap system. Also,
I've used WD hard drive for 3 years, and never had any problems. You can get a 160Gig for around $50.I recomend 2 drives. Make sure you get at least 2 sticks (1gig each) of mem that are the same, so you can use Duel channel. They have to be the same.
As for your GPU, maybe a 8800gt 768mb. It has a lot more power and speed than mine if you need it. And since
your going for X2, i would recomend the top processor 6400. Or, you can get a motherboard that supports both
X2 and Phenom chips. Make sure to check that MB supports max HT for the phenom. I haven't checked out the MB
you have chosen but should be AM2+. I use Newegg.com all the time. You should be able to find some good deals there!
Remember, if you use 2 8800GTs, you will also need alot of power. And to be honest, most games do not
need all that much power unless your a fanatic for details. Frame rates in the range of 30-60 are fine. My Oblivion
AVG is 48fps( low-34, high 68 outside). You don't need 100+fps to play any game!