PC gaming requirements

[PrayForDeath]

Get a Radeon 7750.
Your power supply won't have a 6 pin connector for a power hungry video card, and I've heard Dell even deleted the molex connector on their Inspiron line, so you can't even use a molex to 6 pin adapter. With that being the case the 7750 is the fastest card you can get that is powered by only the PCI-E slot. It only uses ~55W so it shouldn't overload a Dell PSU.

Best advice so far. 7750 has great balance between power consumption and performance. It's guaranteed to work (and fit) with your PC. And it won't be overkill for your CPU.