Hey Andy, First I have a pretty simple solution that might work. In Outlook 2000 go to Tools > Options > Mail Delivery and make sure that "Send messages immediately when connected" is checked.
My second possible solution is to change your Outlook install from Corporate/Workgroup to Internet Only. To do this go to, Tools > Options > Mail Delivery > Reconfigure mail support. Select the Internet Only option and click next. It will ask you if you are sure you want to make the change and tell you that Outlook will need to be restarted for the change to take place, click yes. Once you restart Outlook you might find that a few little problems have gone away. This, of course, will only work if you use internet mail only, not if you are connecting to an Exchange server.
I would like to know if this has helped you at all, would you let me know? Good Luck!