I installed Office 2000 on Vista HP and Outlook wasn't working 100%. I got WAB.DLL errors anytime I tried to use the address book (which outlook does anytime you attempt to write and send a message).
I tried manually adding wab.dll and wab32.dll to the system, but no luck.
Other programs, word, excel and power point appeared to work correctly with light usage. I didn't use them much though.