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Also make sure your PSU has true 8 pin PCI-Express connector rather than a 6+2 pin connector.
This makes no sense, hardly any decent modern PSUs come with 'true' 8 pin connectors rather than 6+2s...
Also that card is very power hungry compared to the performance it offers.
Considering the rest of your rig I would suggest going for the 5770 (or maybe the GTX 460) as 95thrifles suggested. Even with the 5770 you'll be somewhat limited by your CPU in games.
edit: just checked the specs for the Hiper PSU seems you have 2x 6 pin (no 8 pin or 6+2 pin) so I definitely wouldn't suggest going for that 9800 GX2.