If you get this error in Outlook 2007: "Could not install the custom actions the object could not be found", it's because somehow you have a custom form installed on your machine that has gone south. I think the custom form might be an Exchange-based distribution, since I've never installed any custom forms.
Anyway, first close Outlook. If you're on Vista, go to "C:\Users\[UserName]\AppData\Local\Microsoft\FORMS" or on XP "C:\Documents and Settings\[UserName]\Local Settings\Microsoft\FORMS". You may have to make hidden files and folders visible to see this directory. Once you find the directory, blow everything in it away. Then relaunch Outlook.
Now enjoy your time in Outlook. It's so aw3some!!11!