how many amps does the video card require? The manual/specs should tell you that.
Once you know that, check your power supply and see how many amps it can supply on the 12v leg. There should be a big label on the P/s that will tell you the amps for each leg. If you P/S can supply the required amps, then it may work depending on what other hardware you have, ie: how many other cards, hard drives, etc, etc.
However, if you can get a P/S for $40.00, I'd check that out.
Wabb