Do you need to disable an addin or have an addin that isn't loading? Look for it at Tools, Options, Other tab, Advanced button. Some addins are listed in COM Add-ins, others are under Add-in Manager.
If the add-in isn't listed in either location, you'll need to edit the registry at HKEY_LOCAL_MACHINE\Software\Microsoft\Office\Outlook\Addins\ to disable it.
If you use Outlook 2003 and have addin that isn't loading, look in Help, About, Disable items. When an addin causes problems when Outlook loads it disables it for you.