It has been a very long time but it is finally here !
The System Center Operation Manager (SCOM 2007) Management Pack for Exchange 2007 has been released ! You can download it from the following url : http://www.microsoft.com/downloads/details.aspx?FamilyId=1A83E112-8677-4E03-83C3-F1B7EBFC3A4B&displaylang=en
If you want to download more administration pack for SCOM 2007 you can browse the catalog at the following address : http://technet.microsoft.com/en-us/opsmgr/bb847850.aspx
All the best for the monitoring of your Exchange 2007 infrastructure!