I think it will be fine. My kid has a similar setup with similar power supply.
Currently i have this configuration for my desktop:
Intel P915GAV mobo
Pentium 4 3.0 GHz
1.5 GB DDR RAM
1 x 320 GB 7200rpm HDD
GeForce 6200 TC GPU
1 x DVD-RW
1 x DVD-Rom (Optical Drives are connected via Y-cable splitter (power))
500W Power Supply
I'm planning to upgrade my GPU to a GeForce 7900GS and ADD another 320 GB HDD... both these need to be directly connected to the power supply, meaning i'm going to use another 2 Y-cable splitter for them. is my power supply going to handle all these? And i am a heavy computer user... 24x7 use of PC and maybe an 8 hour rest every week or two...