MSSQL-to-MySQL - description from Softdepia.com:
MSSQL-to-MySQL is a program to move MS SQL databases to MySQL server. Depending on your privileges on the target MySQL server, you can either export MS Access data into new database, or overwrite the contents of an existing MySQL database. All MS SQL data types and attributes are supported. The program works with all versions of Unix and Windows MySQL servers.
MSSQL-to-MySQL is a "Free to try" program. You can download and try it for an evaluation period.