You might want to get the non OC version as I doubt you would see much difference between the TI and TI OC. Maybe a frame or two per second better? That aside, you could upgrade the PSU as long as its not proprietary. From what you said in regards to the 250W PSU, it looks like you have the desktop version and thus need a half height card, not a full sized card. I'm not sure of anything that is half height and of decent power. If you have the mini tower then the card should fit just fine.