There's no much different between 256M and 512MB DDR PC2100 in my computer. I felt the big different when I replaced my 128mb to 256MB.... my computer can take a breath more freely. Most of the time I open 5-8 applications at the same time (excell, words, Internet explorer, yahoo and msn messenger, Minitab, SAS, statransfer and watching TV with pinnacle), I still have my computer running flawlessly either with 256MB or 512MB.. barely seen the differences. Of course if you have extra money, it's time to buy more sticks... my expectation, memory prices will still rise until the end of this Summer.