Hi

this whould solve your problem

CONVERT command

A. Convert a SQL Backup file to a Microsoft Tape Format file

-SQL "CONVERT 'C:\Backups\pubs.sqb' TO 'C:\Backups\pubs.bak' "

http://www.red-gate.com/supportcenter/Content.aspx?p=SQL%20Backup&c=SQL_Backup\help\5.4\SBU_Toolkit_syntax_egs.htm