I'm not that great with ME... But, in some versions of Windows you can right click "My Computer", "Properties", "Advanced", "Performance Options". From there you can configure the system to be optimized more for applications or background tasks. If it is set to background tasks, you might want to change that to applications and see if that helps.

It could be RAM going bad. Could be something eating RAM (a program takes it and doesn't give it back on exit). Is it just as bad right after you reboot? Or does it get worse over time after a reboot? Does it work right in safe mode?