How to prevent SQL Log from being too full
A couple of things you can do.

Your database is probably in full recovery mode. This is why the log file does not get re-used. Now if you DON'T need transaction log backups you can set the recovery mode to simple. Your log file will now re-use itself in simple mode. If you DO need transactional log backup i.e. point in time recovery then you will need to actually DO transaction log backups to re-use the log file.

Please be aware that this setting has a MAJOR impact on how you can perform disaster recovery and you need to make sure that the setting matches your disaster recovery needs. If you database is so busy then transactional backups are probably better than simple recovery mode. 

Without transaction log backups you will NOT be able to do point in time recovery. Thus you will lose A LOT OF DATA in the event of a disaster.

Go read about transaction logs and recovery modes here: http://msdn.microsoft.com/en-us/library/ms189275.aspx

Now there is something else you need to keep in mind. Virtual Log File fragmentation. It is going to be something very important to understand and master. Kimberly L Tripp has a very very  usefull blog entry about this. You can read all about this very helpful topic here: http://www.sqlskills.com/blogs/kimberly/post/transaction-log-vlfs-too-many-or-too-few.aspx

Keep in mind 50-100 transactions a second is not a lot. Also a BIG transaction log file is not always a bad one. There is more to log files than just logging transactions. Go read about it. It is a topic worth mastering.