You you are going to implemend IE’s add-on list control here is a good place to start of allowed CLSID’s
http://support.microsoft.com/default.aspx?scid=kb;en-us;555235
Tag: ie
IE Add-On HTC Components
If you are implementing IE Add-On blocking via the registry or GPO it will block all .HTC (HTML Components) files you need to allow the following CLSID {3050f4f8-98b5-11cf-bb82-00aa00bdce0b}