Process Explorer is another tool in my arsenal when troubleshooting a COM Addin loading problem. Often times developers will think that their Addin is not loading, when in fact it is. The problem is that the Addin is not behaving as expected (e.g. “It’s not adding my toolbar button, when it should”). To confirm that the Addin is being loaded I use Process Explorer. Process Explorer can be downloaded here http://technet.microsoft.com/en-us/sysinternals/default.aspx or if you have Windows Vista you can just run the following command: Start > Run > \\live.sysinternals.com\tools\.
Once you have downloaded Process Explorer it is easy to use to verify that Outlook is indeed loading your COM Addin. Just run it and select Outlook within the upper pane. Then select View > Lower Pane View > DLLs to see the list of DLLs within the Outlook process. If you find your DLL, you know that Outlook has at least loaded your DLL. The next thing to do is to figure out why your Addin is not behaving as expected.