I think it could be any number of things.
I also have 2003, and was finding that it would crash every 20 minutes
or so after it was deployed on new workstations at my workplace. Turns
out there is a screen capture program also installed, that has a
plug-in for Outlook. Once that plugin was disabled, Outlook became
stable again.
You're going to have to narrow it down by either looking in the event
viewer for error messages, looking for other running programs you can
close to eliminate them from the equation, or duplicating your
installation on a fresh machine, installing Outlook first and other
apps after, using Outlook frequently during the process so you can see
if/when it starts to bomb.
Cheers,
DW