If it is corruption, nothing can be done, that backup's not restorable.
Was it taken with native backup (backup database... to disk = ...) or was it taken with a 3rd party tool (SQLBackup, LiteSpeed, etc)? Was hyperbak installed on the server?
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