Would an Antec Earthwatts 500 Watt ATX PSU work? It has 2 +12V rails that will support 17 amps each.
That should work with what you have. The Earthwatts 500 is a good PSU. The only potential problem is that it won't leave much room for expansion, and if you ever wanted to go SLI or Crossfire, it would be too small. But only you can determine if you ever want two video cards.