Yeah you'll need a new Power Supply for sure. I'd get a new PSU and Case if I were you. You'll need a good 400watt PSU I'd say. Is your motherboard a Micro ATX as well?

I have a question about your 2.53ghz CPU also, is it a Pentium Celeron? If so you're going to need to upgrade that as well, becuase it'll bottleneck your graphics card to hell. If so, just upgrade your whole PC from scratch