Select the cell you want to enter data into, click FORMAT in the menu and
select FORMAT CELLS. Click the PROTECTION tab in the dialog box and remove
the check from the LOCKED check box.
Click OK to exit.
Once you're back in the worksheet, click TOOLS in the menu and select
PROTECT SHEET. Remove the check mark from SELECT LOCKED CELLS and if you want
to add a password.
Click OK to exit.
Now the only cells that are tabbed to are the ones you unprotected earlier.