depends, is your psu of quality, and has a 6 pin connector? according to This
the card would eat up too much of your psus wattage on load. and that would be pushing it. unless you had an EXTREMELY high quality psu that can push past its labled wattage, you are going to need a new one.
if your planning to no overclocking at all and never upgrading parts in the future, get a 380-430w certified psu(I emphasize the word certified, preferably bronze at the least, common choice would be an antec earthwatts for low wattage and works well)