You'll have to open up your computer to put the graphics cards in so why not open it to check
on the power supply? I'm sorry, but there is no way to check it without physically looking at
it or getting the model number from someone who has seen it. There are programs that will
monitor the stability of the 5V, 3.3V and 12V rails but nothing that will give you all the
specs you need.
Do not merely check the power supply's wattage rating. There are 500W PSU's that cannot
support high end graphics cards. You need to open it up, get the manufacturer and model
number, then google that to find the specs. You need to look for the number of amps on the
12V rail. If it has multiple, there's a good chance it will, then you can roughly add them
together to get the total. This needs to be above 30 amps minimum, preferably above 36 if
you're going to overclock. That's just for one card. For two you need to shoot for above 40
Also, it will not support two ATI or Nvidia cards, it's one or the other. Nothing out there
supports both Crossfire and SLI, only one or the other. That is determined by your chipset.
If you have an AMD or Intel chipset then you can Crossfire. If you have an Nvidia chipset
then you can SLI.