It really depends on what else you are running in your comp. VGA cards are generally powered by the 3.3V rail, so you should be fine with any sort of power supply as there is usually a lot of overkill with the current on 3.3V in this day and age.
The AMD64 series actually consumes less power than the thoroughbred AMD Athlon series. So if your current power supply can support an athlon 2500, then your new one should be able to support this one. What are the specs on your current power supply? Look on the side and read off what is under +3.3V, +5V and +12V.
Also take a look at this page
you should be able to work it out from there