As Gail mentioned, figure out what is causing the log file to grow, otherwise if it happens again you will be in the same boat.

Something wanted the log file to grow to 5GB so if it happens again and you have shrunk the file already it will regrow to 5GB.

Then you might get away with using DBCC SHRINKFILE

http://support.microsoft.com/kb/307487

Otherwise restart SQL or add more space.