The MOM 2005 agent is now supported on Windows Vista (Enterprise, Business & Ultimate). See http://www.microsoft.com/technet/prodtechnol/mom/mom2005/vista.mspx
The MOM 2005 Administrator and Operations consoles have also been tested and are not known to cause any issues.
A KB article confirming this will be available shortly.
Clive Eastwood - System Center Operations Manager Supportability Program Manager