If you are shrinking database files frequently, then you have bigger problems than your shrink operations or your applications truly need the space and you need to get the bean counters to release a few so you can grow out your disk accordingly.
This is a common problem.
You should have a backup routine; as part of this, you should set the translog to be truncated. This will keep the file down to a reasonable size.
Here's a set of instructions posted by another spicehead. http://community.spiceworks.com/how_to/39965-shrink-large-transaction-log-files-in-sql-server-2008
It can be done using the SQL studio management tools or using a script.
If you don't have sufficient disk space on the existing drive, you can actually set it to backup to a different local drive or even a network drive. You can usually do it when users are accessing the DB and although there may be a slight drop in performance, they probably won't see too many issues.