Slow Performance Windows XP/Outlook

I frequently have issues with having to wait for my PC to respond when using Outlook with Windows XP. This usually happens then I am responding to or forwarding an email. I can’t do anything for 30-60 seconds, then suddenly, I can. I check SystemPerformance, and many time CPU usage spikes to 100%. This happens whether or not I have other applications open, and other applications are usable. I have two profiles set up in Outlook, one for two different emails. I have three PST files. Can you help me avoid having this wait time?