I used to have a 550w one in my old rig powering an A64 3400+, 1GB pc3200, Asus V9999GE Gamer Edition (souped up 6800) a pair of hard drives, a CDRW and a DVDRW and i never had a problem with it at all. Naver overheated, no strange noises and was stable and very quiet too. Not bad for £29. If you are going to get one then don't get it from a well known high street/buisiness park rip off merchant that has purple signage.
You should however get the best psu that you can afford. After all if it goes then it could take most of your rig with it. For gods sake don't buy a Qtec.