If you're anything like me, you don't like having programs you don't use start up when you open other programs. If I wanted to open it, I would open it myself or have it start up when my computer boots up. I had a tech request recently that dealt with Messenger starting up when Outlook 2002 starts. Here's how to disable that:

Open Outlook and select Tools from the menu bar
Under Tools, select Options
Select the tab named Other
Towards the bottom you'll see a section named Messenger
Uncheck the box next to "Enable Instant Messaging in Microsoft Outlook"
Click Apply
Restart Outlook

Now that little messenger icon next to your clock shouldn't pop up again when you open Outlook 2002