It's possible that it would still be adequate, personally I would want some second opinions, and for anyone to give you a second opinion you would have to tell us what hardware was used with it before (CPU, PSU specifically) and exactly what PSU it is.
I was asking about the PSU, but seeing as you said it's like a mirror on the outside, I think I know which one you mean now. As the ATI 9600 apparently only uses 75W of power I'm thinking that it wasn't taxed too heavily that power supply.
I'm doing research on the PSU that I think you have. I think it is the Ultra X-Connect, as it is very shiny/mirror-like.
Yea the X-connect 500W has received many favourable reviews, altho they are dated around 2004-5. So it should be able to last for awhile longer, altho it would be a wise investment to replace at some point, if not now.