You will have no problem running all your office applications on a 9500GT.
OTOH, if you will be playing demanding games like Crysis, get the GTX275 if you can afford it, as the 9500GT will run and hide.
The best choice depends on what you will be doing with your PC, and the resolution of your monitor.
What PSU do you have? An Antec Earthwatts 500 will have no problem with any of them; an Apevia/Aspire "680W" model will likely melt.
Drop that no-name PSU ASAP! Look for Antec, BFG, OCZ, PC P&C, Corsair, and Silverstone (unless in a 220v area). At least a 550W, with either the 250, or 275 (Tho I'd also look at a 4870, or 4890 as alternate options).
Slightly different advice: Use your psu if you own it, but if you get flaky performance look there to find the problem first. If you've got a Kia, there's no need to toss it and buy a Lexus if it will get you to the grocery store.
If your price for the 250 is $US, look at this one, one of the higher priced versions of the card: