Depends on how much it takes out of power i'm running a 600 WAT power supply with a GTS 450.
So get a power supply that is 500+ Watts
If you would like here is a good power supply: Rosewill RV2-600 600 W ATX12V v2.2 / EPS12V SLI Ready Power Supply
50$ on Newegg, thats where I got mine.
But remember the PSU is the part that you need to spend the most on.