Please read through this - Managing Transaction Logs[/url]
If the log file has grown too large, a once off shrink to bring it back to normal size is fine. Log backups don't shrink the log, just allow the space inside to be reused.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability