not sure abt outlook 2003 [office xp] but u can minimize outlook in ofiice 2003 to tray...
try this application *www.neowin.net/comments.php?id=27886&category=software]TaskAwitcherXP
it's replacement of alt+tab function in explorer... also eats very less resource ~ 400kb ... very nice tool... after installing configure it's settings and check
"minimize windows to tray on right-click on minimize button"
done!... not only for outlook but for all progs u want to minimize