The OP wrote:
I have a 300 watt PSU powering AMD Athlon 64 3000+, 512Mb PC3000, GeForce 6600 GT AGP and a seagate 200 gb sata drive.

johns wrote:
Yep, that is a joke to run the hardware you have. Go
out and buy an Antec SLK1650B case with $350
watt supply that sources 21 amps on the 12v rail.

How much power does that video card use?

With the possible exception of the video card, that system's power
demands are meager.