Spec sheet is here, and I plan to burn no more than $60 in upgrades
- Intel Core 2 Duo E4500, 2.2GHz
- Upgraded to 4GB DDR2 RAM (4x1GB IIRC), speed unknown
- Either Win7 HP x64 or WinXP Pro x32, haven't decided yet.
- 300W PSU, does NOT have a GPU power connector (i.e. cannot take an 8800)
- Only other crap that needs power is a CD drive, a single HDD, a card reader, and the USB ports.
I would say that the main obstacle here is the PSU, which limits upgrades like it's nobody's business. I'm not prepared to drop $40 on a new one, then $60 on a GPU, as I'm too lazy to rewire it (and a $60 GPU probably can work with the 300W constraint anyway).
TL;DR: Best GPU that can fit within a 300W PSU constraint. Go.