Hello, never mix different types of RAM modules, it really causes hell. I have been experiancing crash problems in new games puke: (exept HL2 strangely) and according to realblackstuff, it's because I have two different Ram Modules, 256mb PC2100 (although it says PC2300 in CPU-Z) and 512mb of PC2700. Its not the size that matters, its the type/clock speed of the modules. In old motherboards you could slam in whatever you wanted but thats no longer the case, to avoid problems, all RAM modules must be of the same speed, size doesn't really matter, but a matched pair of modules can have minor performance gains. Keep this in mind when upgrading RAM.