ANSWER:

This really depends on things like the efficiency of the power supply and how much stuff you have in your computer.

If you are running a relatively bare bones system without a ton of bells and whistles then you would most likely be okay.

That being said you should be fine, the worst that is likely to happen is some system instability if you do demanding things that require more power than the PSU can supply.

BSOD and the like.
So I would try it and if it works then huzzah!

by Money Loo from http://superuser.com/questions/428181