Great script! Thanks for postingit. One minor change I would make would be to change the subquery to resctrict the database id to less than 5.
I ended up with 2 entries because I had a database named SMSDB.
Here is the editted subquery:
(select left(af.filename,3)from sys.sysaltfiles af where af.name like '%MSDB%' and af.fileid = 1 AND af.dbid<5) as 'Drive',