Slow performance for Microsoft Outlook

My computer got upgraded to Windows XP and is using Microsoft Outlook 2000 SP3. Since the upgrade, my e-mails are very slow in response. It takes a very long time to receive e-mails even from someone next to my desk. It used to be almost instantly but now it is slow. Another coworker’s computer was upgraded and same thing is occuring. Any ideas why the slowdown has occured? How can I speed this up back to normal?