Ok I just built a good, dual core gaming computer for $811 CAD.
All component prices are from
http://www.canadacomputers.com/ and are rounded up to the nearest dollar.
Intel Pentium 805D 2.66ghz Dual Core - $160
XFX nVidia GeForce 7600GT 256MB - $240
OCZ DDR2 PC2-4200 533MHz Value Series 1GB (2X512MB) - $102
Seagate Barracuda 7200.9 SATA NCQ 3.0Gb/s 160GB 8MB Cache - $83
322E Black Case 400w w/ Windows, USB - $20
SilverStone SST-ST405 400W Low Acoustic (Silent) Power Supply - $57
Asus P5ND2-SLI - $109
LiteOn SHW-160P6S Black DVD+R/RW 16x8x DVD-R/RW 16x6x DVD+/-R DL 8x4x DVD Writer Bulk Pack - $40
Total: $811
I will note that you would have to replace the powersupply that comes with that case with the one I added in here.
You will also have to order some of these parts. This still leaves you with $188 to buy an OS or any extra components if that's nessicary for you.
The speed on this is lower than the futureshop computer but the increased graphics card would easily nullify that once you got around to gaming.