Move over let me through. First off 200 watt PSU thats Compaq for ya. AMD CPUs will let you know real fast if there isn't enough power. But most video cards use little power to run unless they're like the new ATI 9800'* that have a power connector on them. But signs that you need a new PSU would be weird graphics like blocks or lines on the screen but that could also be bad vid ram, but most common are files corrupting, system won't post, system locks or blue screens. In my experience 200watts and AMD don't go together but if the system seams to run ok than no need to fix it.
And yes thats an ATX system if you get a new PSU get one that is tested for P4'* and AMD'*. The AMD are very picky about clean power please don't buy a bargain bin PSU you'll just end up buying a better one in a few days.
As for how much power 300 or 350 is good more is just likely over kill but you can put as big as you like the system will only use what it needs.
Thats A+ Server+ Compaq APS MCP and 8+ years as a computer hardware tech speaking.