This approach has worked on most of our PC's that are severly short on RAM. It is just a suggestion, you may have already tried the below items.The problem sounds an awful lot like "Disk Thrashing". Which is basicly that there is not enought RAM to accomidate all the stuff that is going on so the system is constantly writting to the hard drive.. Also check that the performance is set to "Adjust for Best Perforamnce" and not "Adjust for Best Appearance" or "Let Windows Choose...".