If it was working and now is not, you likely have picked up stray processes running in the background eating your memory/cpu. If you know what you're doing, you can go in and remove them. If not and you want the easier way out, I'll agree that adding some RAM is a good idea. I'd also check to make sure you have plenty of virtual ram set up.
You might also want to DL and run AdAware and Spybot Search and Destroy (be careful, don't install something called just Spybot)
Bryan
