GPU upgrade for better gaming?

Hello all I have a pretty old system layin around that I would like to do some gaming on, my budget is EXTREMELY Limited due to high shipping cost, customs tax, etc.

APPROXIMATE PURCHASE DATE: 2-3 Weeks from today, No More than $100 USD (Dont think I qualify for rebates)

USAGE FROM MOST TO LEAST IMPORTANT: Gaming (Dragon Age 2 coming out soon)

CURRENT GPU AND POWER SUPPLY: Onboard Intel Graphics Media Accelerator X4500 & A-Power AK 680W 20+4-pin ATX PSU

OTHER RELEVANT SYSTEM SPECS: E5700 @ 3.00GHz, Biostar G41D3 Intel G41 Socket 775,OCZ Gold 4GB (2x2GB) DDR3 RAM PC3-6400

PREFERRED WEBSITE(S) FOR PARTS: Amazon.com because I live in the Caribbean

PARTS PREFERENCES: Not really

OVERCLOCKING: If needed SLI OR CROSSFIRE: No

MONITOR RESOLUTION: 1280x1024

ADDITIONAL COMMENTS: Nothing Fancy Need...Im just looking for some good framerates