Outlook XP sucks a great deal less than Outlook 2000. I hate them both, but it's retarded that Microsoft's mail client can be configured in such a way that it can't talk to an Exchange server, which is absolutely possible with Outlook 2000.
Also a full install of Office XP has a smaller footprint on disk. ... and I think it runs a little faster, probably the result of more multithreaded functions.
Office 2003, though, seems absolutely worthless if your PC doesn't have 512MB RAM, something I've been suffering with at work for the last few weeks.