You probably have a similar pc to mine (Dell Dimension V350). Yes, I admit it, I have a dell, well, it was a dell, the only thing that is still dell is the case, psu, and mobo. Anyway, mine uses the ar440bx mobo, wich is absolutely impossible to find anything on, seeing as how it was built specifically for dell. Now,the 440bx chipset will run 768 megs ram max i think. Dell states that the pc will accept 384mb (128 x 3), but i have run 512 (256, 128 x 2) in it fine. So, 256 x3 will work, but im not sure about 512. one 512 may work, with a pair of 128, but that's probably the max. Only one way to find out.