to install the schema snapin if you havent already, go here...
http://www.microsoft.com/windows2000...all_Snapin.htm

for more info about master roles...
http://www.microsoft.com/technet/tre...ag_ADFSMOs.asp

I believe most of the single master roles will automatically transfer when you demote a domain controller, not sure about the global catalog.

I had a domain controller die completely on me once, and had to sieze all of those roles forcefully using ntdsutil from the command line. That wasnt much fun...