Yeah - I think it stems from the fact that Outlook is a P-O-S.
Recently did a clean install of XP and Outlook now starts up reasonably sprightly compared to before...
... until I get a few messages in the inbox again no doubt.
Same thing happens with Word - OK when you first install it, but after using it for a couple of months takes ages to open even the simplest documents.
Bill Gates in league with Intel and Western Digital, methinks.