I'd say it depends on how well the power supply supplies power.
Believe it or not, I have a ASUS 250W PS that runs a Duron 800, three HDD's (40G, 20G, 10G), 2 optical drives (CD-ROM, CD-RW), four case fans, a Mini-Copper Orb CPU fan, and a host of add in cards.
And it's never missed a beat!
Yet I have friends who have problems with their cheap 400W power supplies!!
So, try it with a burn in program, and see how well the PC copes with full load.
Cheers
Mick