The first thing we need to know is what the EXACT model of your power supply is, because if you have a 625w power supply then it is VERY old. All of the units I know of that are based on 625w platforms are extremely old and should not be used with any new graphics card you might install. That means the budget is going to need to include a new PSU as well most likely. If that unit is more than five years old, and I'm quite sure it is, there is no way anybody could recommend continuing to use it.
Also, I can't seem to find anything on the Thermaltake vl9000, can you link to it's product page or provide the correct model number? It might also just be so old that there is nothing out there on it anymore.
What kind of budget are you...