7300 = CRAP.
As far as PSUs go, for a lower end video card you don't need to upgrade the PSU. Most medium-high cards say they require 350W or more, and you already have that.
I would say the HD3650 is a good call for AGP, but if you can get your hands on one the Ge7600 (GT preferably) will more than keep you going for another 3-5 years.
Also, don't go around buying low-end, cheap, replacement parts for your CPU, your RAM, etc. You'll end up prolonging your PC life a little but you're spending money on a system that really won't get much better than what you currently have now (aside from the dead video card, I mean!)
Get the video card, but save your pennies. For $600 you can get a new PC capable of running any game today. For $800 you can get a new system capable of running any game today at 200 fps and with high res and FSAA. Save those pennies!