The problem with just saying you have a "M52BC" computer is those computers can be configured multiple ways. This makes it hard to get solid information on it. What CPU does it have?
The wattage of the power supply will be on a label on the power supply itself. So shut down the computer and remove the side of the case and look inside. It'll say something like "300W", and while you're at it look at the 12V output, it'll say something like "20A". Those two numbers will help determine what kind of card you can use.
Right now I'd be willing to bet a 460 will work.