The Microsoft Knowledge Base article KB 293445 Has a list of references to protection information.
Microsoft Excel provides multiple layers of protection to allow you to control who can access and change your data:
Worksheet protection: You can protect elements on a worksheet (for example, cells with formulas) from all user access, or you can grant individual users access to the ranges that you specify.
Workbook-level protection: You can apply protection to workbook elements, and you can protect a workbook file from being viewed and edited. If a workbook is shared, you can protect it from being returned to exclusive use and prevent the change history from being deleted.
... articles address some of the more frequently asked questions about workbook and worksheet protection in Excel:
How can I grant only a few users access to a range in my worksheet?
Why are users not allowed to edit the ranges that I established permissions for?
What new features are available in workbook protection?
Why don't the permissions that I set on ranges in my worksheets carry over to Windows 98 computers?