Yes the 2600PRO is fine. I have one that worked fine on a 300watt for a long time overclocked playing CoD4. I eventually got a 480watt PSU because it was cheap at the store nearby.
I got mine overclocked to 650 core, 475 memory and it plays CoD4 at 1280x1024 (no AA/AF, I hate it) at 45-60fps average.
Gateway GT4016 Desktop | CPU: AMD Athlon 64 3700+ @ 2.2GHz | RAM: 2GB (4x512MB) | HDD: 1x200GB, 1x120GB | Video: ATI HD Radeon 4850 512MB | OS: Vista Home Premium x86 SP1, Mac OS X Leopard 10.5.6