Try "backup log <log_name> with truncate_only" to reduce the log size. This reduces the log size by truncating it. Also you can change the logging type by right-clicking the database and select properties, click the options tab, and in the recovery section, change the drop-down box to simple. This should help your log not grow so fast. The tradeoff is that it doesn't log as much information as you normally would want it to log.
Hope this helps,