ive posted this before, but ill say it again anyway..

research parts and stores through the internet and then build your own (or have the boxes built at the store if youre not comfortable assembling). you will end up with much better systems, a similar (far easier to claim) warranty and much more available support.

after a quick look through Newegg.com as a reference for prices..

2gb 667 Corsair RAM - $100
GeForce 8600GT - $90
Motherboard = Gigabyte DS3 or Asus P5B - $100/$130ish
CM CAC-T05 case - $49.99 (430w PSU incl.)
generic 18x DVD - $30
17" LCD - $100
--
<$500.

thats just a quick check. im sure if you research a bit you could find the parts cheaper. any decent retailer will give you a 24 hour hot test with 1-2 year RTB warranty for assembled systems. also remember that owner run business are often willing to negotiate (within reason).. the people i went through knocked $50 off the cost of each system and threw in a free 8 port switch, because i purchased 4 systems and a bunch of peripheral gadgets in one order. all up i got 4 systems, KVM, G15 keyboard, G5 mouse, switch, cables, 4x 17" LCD's and a 28" viewsonic LCD for under $3900 AUD.