It's called a clsid (class identifier).
http://www.windowsitlibrary.com/Content/368/13/1.html

I don't know about all of them, but you'll find some of them here under "namespaces"
http://www.mvps.org/serenitymacros/icon.html

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What the Dormouse said
http://forums.techguy.org

[This message has been edited by Rog (edited 01-06-2002).]