Use the Tools-->Protection-->Protect Sheet command. You can assign a
password (which you'll have to enter twice) so that only authorized users
can unprotect the sheet.
Before protecting the sheet:
1. Select all of the cells you want the users to edit and access the
Format-->Cells-->Protection Tab. Uncheck the "Locked" option.
The assumption here is that none of the cells they'll be editing contain
formulas.
2. Select all the cells that contain the formulas you want to protect.
Tip: You can quickly select all the formulas in a worksheet using the
following:
a) Click Edit-->Goto (or press F5)
b) Click the Special button
c) Click the Formulas option
d) (Optionally) Uncheck any desired formula types
e) Click OK
3. Once the desired formulas are selected, access the
Format-->Cells-->Protection Tab again
4. Check the Hidden option, which will not allow users to view nor copy the
formulas when the sheet is protected.
5. Click OK
6. Protect the sheet using the command described at the beginning if this
response.