Workbook protect

File|Save As
In the Save As dialog box you will see a button called Tools

Open the Tools box gives you an option General Options two further protection options are

1.Password to open
2.Paswword to Modify

Enter a password to open & click ok... then carry on saving the workbook to the desired location

When yo next open the workbook you will be prompted for a password in order to open it.

Be aware that XL's password security is not too difficult to break, although it should be enough for most potential users...