you will need new RAM because you have DDR RAM, and not DDR2. i made a list of parts that is just a tid bit over your budget...
- Motherboard - ASUS P5N-E SLI - $132
- RAM - OCZ platinum Rev.2 DDR2800 2X1GB - $80 ($45 after rebate)
- Power Supply - Antec Earthwatts 430W - $75
- Video Card - 8800GT - $254
Total - $541 (excluding taxes and shipping)
***all prices in CAD and were found at http://www.ncix.com/i would like to know EXACTLY what your CPU is, to see if it compatible with the new motherboard. to find your CPU make/model go to Control Panel, from there select System, under "Computer:" it should tell you the make/model of your CPU. if not, select the "hardware" tab, select "device manager", click on the plus sign next to "processors", there it should tell you your CPU.