Messenger 5 silent install forcing reboot w/ Outlook open

[AC]

I am trying to perform a silent install of Windows
Messenger 5. I have a script that closes previous
versions of Messenger if they are running prior to the
install of version 5 and it works fine. However, if
Oulook XP is open while performing the install Messenger
tries to force a reboot. I am currently using the /Q
parameter (i.e. c:\mmssetup.exe /Q). Any ideas on what
is causing this? Is there another parameter I should or
can use?