Originally Posted by Razorfinger
Is a 300W power supply good enough to run a 6600 AGP with 256MB?
I hate to sound clichÚ, but you shouldn't risk modern hardware with power supply wattage that was considered adequate for computers of 5 years ago. Look at it this way, out of all the parts on your computer, the PSU is the one component that when "inadequate" can actually damage or destroy other components.
It "may" be fine, however, I suggest making your next upgrade a nice 500+ watt PSU that you can begin building the rest of your computer around. Pay attention to the +12v rail. Sure, it may be overkill for your current machine, but too much can't hurt and it'll last you another 3 to 4 years in the future