did you get taht powersupply from an OEM system? HP/Compaq? I used to have one thats 250Watt. and it ram couple Disk drives, 2 fans with lights, HDD, video card and floppy and a P4 2.4ghz HT. did fine for a few years. actually, it jus recently start to give out. Id say you'll do fine 80% guaranteed =P
also, as donnagual has mentioned, its not always about the watts. the most important are 12V rail, 5V and 3V (respectively) and how many amps they can handle and the quality of the PSU of course. stay away from cheap PSUs. sometimes price catches ppl off guard and they end up with a PSU that blows and/or dies n leaves them confused