That'll be more than enough. I'm running a P4 2.6C, 1GB DDR, 2 hd's, Radeon 9600, GameTheater XP, DVD/CDRW, floppy, and 2 case fans off of a 300-watt PSU.
The vast majority of systems can run fine on quality 300-watt PSUs. It's efficiency that matters, not just the big wattage number. From what I've read, Sparkles are a good brand of PSUs.
You'll be fine.