Microsoft has added support for Win7 and Server 2008 R2 clients in SMS 2003 SP3.
More information can be found here
http://support.microsoft.com/?kbid=974014
This should be used as a stepping stone as people move from SMS 2003 to SCCM 2007 or even V.Next due out sometime next year. Since main stream support has ended I would recommend people look at moving not just because support has ended but because the added benifits that are in 2007 Sp2 R2.
If you intend on staying with 2003 and jump 2007 then I would recommend that you download the ConfigMgr 2007 R2 VHD http://www.microsoft.com/downloads/details.aspx?FamilyID=e0fadab7-0620-481d-a8b6-070001727c56&displaylang=en
to play with and see how it all works so you will be better prepaired for the next version.
