By default when running Outlook XP(2002) it clutters the taskbar, one can make it into an icon on the system tray. This is done with this DWORD in registry :

[HKEY_CURRENT_USER \Software \Microsoft \Office \10.0 \Outlook \Preferences]
MinToTray = 1 (Default = 0, Enabled = 1, Disabled = 0)

Note in Outlook 2003 it can be done by Right-clicking the Outlook icon in the notification area, and select "Hide When Minimized" in the shortcut menu. More Info MS KB833007

Note when having enabled minimize to tray, then it is possible to make Outlook automatically place it self in the systray when it is started. This is done by creating a shortcut to the Outlook icon, which starts Outlook in minimized state. More Info MS KB251340.