I think the RAM will be the fault in this case
If you have more than 1 DIMM of RAM in your motherboard, take one out and test the program, and then test the other one. If one crashes and the other doesn't, you know which one to replace.
If though you only have one RAM chip of 512MB, then you know the culprit already.
IF YOUR MIXING:
If though your mixing the old RAM with the new RAM, this could also be a problem if the speeds, timings are different, as they say to get the exact same type of RAM if you are to have more than 1 chip installed.