Newegg - Power Supply Calculator
Tools like these help us figure out what we possibly need in our Computer.
My Theory is, whatever the site recommends, I add 100W as a buffer Zone for myself.
I've heard Mixed Reviews on the OCZ lineup of Powersupplies, personally speaking the one that I used never failed, but a lot of people who have higher end systems tend not to trust them.
Personally speaking, I would upgrade that Unit to something a little more modern.
Corsair , Ultra , Thermaltake make some decent Power Supply units at good prices with nice warranties. That would be my recommendation.
ST