Convert backup file generated from SQL server to MDF and LDF files?

i backuped a database using Enterprise manager and saved the backup file into DISK wiz name “MyBackup.bak” ..
I want to generate from this backup file two files in MDF and LDF files .Because i can’t restore the “MyBackup.bak” again , I got an error “The media set for database ‘MyDB’ has 2 family members but only 1 are provided. All members must be provided.”.
Please any one can help me … !!!!

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