Microsoft has released a new compatibility pack for SMS 2003 SP3 that’s adds Windows 7 and Windows Server 2008 R2 as supported clients. However since main stream support for SMS 2003 has already ended I would highly recommend that you start migrating to Configuration Manager 2007 SP2 ASAP, and only use this update as a "workaround" until you everything migrated.

More info and download: http://support.microsoft.com/kb/974014

Enjoy.