An easy-to-use application that helps you with recovering passwords from .XLS files is the Atomic Excel Password Recovery. Here you will find a download link for a trial version as well as a review for the program:
http://atomic-excel-password-recovery.software.informer.com/
Actually, to decrypt an Ecel file that is encrypted, you can use SmartKey Excel Password Reovery 5.0. It is one of the best excel password recovery tool in the world and I have used it to decrypted my excel document successfully. More details in: http://www.recoverlostpassword.com/products/excelpasswordrecovery.html
