The reason you can't find it there is that it doesn't live in WBConfig.
If you are on XP, go to the Appearance tab of Display Properties and switch to either Luna or Classic & apply it. The next time you reboot, either Luna or Classic will remain the GUI.
If you're on Win2k or Win9x, go to the Skins tab of Display Properties - you'll see a checkbox at the bottom of the dialog that reads "Prevent Windowblinds from loading at startup". Check that and the system will come up in Classic when you reboot.
Cheers,
Daiwa