it would highly depend on the total system draw in the computer and the quality of the intended PSU. but if you have a single video card 500 watts in most cases is more than enough.
The PSU i`m going to use is a powerlink LPK2-30 500w and yeah it`s only a single video card.
it will work although it is a low quality PSU id just use it until you can afford something of high quality. I would also check if your video card uses pci-e power as you would need a splitter 2 molex to pci-e if that power supply does not have one.