You could either beef up your computer's RAM, or increase virtual memory size. Go to System Properties via the Control Panel, select the Advanced tab, and double or triple the amount of disk space allocated to virtual memory.

Oh, and it wouldn't hurt if you made sure your computer runs as lightly as possible. The way things are nowadays, every time you boot up there is a lot of stuff that loads automatically. Once you get rid of that, you can expect up to a 100% improvement in computer performance.

Sorry if I'm just repeating what someone might have already said earlier - I'm in a bit of a hurry and don't have the time to check.