Han,
You need an ACS for Windows in order to run the migration utility. You can either download the Cisco ACS 4.2 trial version and try loading the ACS SE backup on it in order to perform the migration or you might need to contact your Cisco Account Manager in order to get the appropriate assistance with the migration process.
NOTE: TAC might be able to help you doing a best effort migrating the database for you to 5.x and providing you the 5.x backup, however, the Migration utility is not supported by TAC. Again, as best effort is always performed but TAC will be assisting on an unsupported scenario.
Hope this helps.