There has been a change in SQL 2005 SP3 that can impact the installation of OCS 2007.  This does not impact OCS 2007 R2. 

SQL 2005 SP3 has an update that changes a return code that the OCS 2007 install was not designed to handle.   If you are having to install a new OCS 2007 pool and are using SQL 2005 SP3 here are two possible work around to complete the install.

1.    Install EE pool from a server that has SQL 2005 Sp2 client tool on a different server altogether

2.    Uninstall SQL 2005 SP3 Backward compatibility and then install SQL 2005 SP2 BC(SQLServer2005_BC.msi on SQL 2005 Sp3 EE server.