482W + 30% =627W, so you'll need a 650W PSU. More if you plan on adding any more hardware components or upgrading to a higher spec graphics card.
If you're not sure which card you want, go
here to compare the features of various graphics card.
For example, go
here to compare the HD2600XT with the X1900GT, and
here to compare the HD3650 with the HD2600XT.