Microsoft supports the use of the Site Repair Wizard to restore a System Center Configuration Manager 2007 site server from a 32-bit Operating System to a 64-bit Operating System as noted in the article About the Site Repair Wizard (http://technet.microsoft.com/en-us/library/bb680393.aspx).
However, there are two possible issues that may occur on a site server restored in this manner. These issues will only occur if the site server was originally installed to the default Program FilesMicrosoft Configuration Manager directory on the 32-bit Operating System.
http://support.microsoft.com/kb/2667543/
List of Public KB Articles and Hotfixes for Configuration Manager 2007 SP2:
