It Should be more than enough.
But, what do you mean by fully loaded?
If you only have 1 or 2 hard drives, 1 to 2 cd drives, sound, video,modem,NIC, Floppy, up to 3 case fans, and the CPU HSF you probably only need a 300w at most. You want be taxing it at all.
If you have more drives, like I...