Beta SDK's available for WSS 3 and 2007 Office System

https://www.microsoft.com/downloads/details.aspx?familyid=BD5C77B0-F556-4136-8730-1D7FEEAE0A42&displaylang=en

https://www.microsoft.com/downloads/details.aspx?familyid=05E0DD12-8394-402B-8936-A07FE8AFAFFD&displaylang=en