You can't really "turn off" the transaction log. Its an integral part of SQL Server. You have two options for clearing the log on a regular basis.
1. You can do frequent transaction log backups. In my shop, we do them every 15 minutes in most cases.
2. You can set the database to Simple Recovery Model. This will cause SQL Server to clear completed transactions from the log regularly. One note of caution: you lose point in time recoverability by doing this. It is NOT recommended for a production transactional database.
Steve