Rolling your own PHP solution will certainly work though I'm not sure if there is a good way to automatically duplicate the schema from one DB to the other (maybe this was your question).
If you are just copying data, and/or you need custom code anyway to convert between modified schemas between the two DB's, I would recommend using PHP 5.2+ and the PDO libraries. You'll be able to connect using PDO ODBC (and use MSSQL drivers). I had a lot of problems getting large text fields and multi-byte characters from MSSQL into PHP using other libraries.
