There's a link in my signature for FS2004 SDKs.  Click it and look for the MakeMDL SDK.  It will have a file that contains all of the tag names.

There is also a little script that you can add to Gmax that will help you name everything in your file without having to open the SDK stuff every time you want to know the names.  Its called TagTool.  Find it here:

http://www.fsalpha.com/home.shtml