Whoa, I didn't notice so many had replied until now. I have to clarify, it came originally with 128MB but we had 2x512 in it when my fiancee used it, but when we gave it to her mother, we took out the 2x512 to save for another system. Anyway, I know that if one stick is, say, 133 MHz and the other is 100 MHz that they both will run at the lower speed. I just wanted to know, in general, if unbalanced RAM (1GB and 128MB) would cause an issue. She says the system is like super-fast compared to before so maybe that's all that matters, eh?