One way would be to select the cell you want to provide access to, go to
Format>Cells and on the Protection page remove the check for "Locked". Then
got to Tools>Protection>Protect Sheet to activate protection with/without
password. Users will still be able to "point to" but not select anything
other tha the unlocked cells.
If using Excel '03 (not sure about XP), you can also use the
Tools>Protection>Allow Users to Edit Ranges feature if more appropriate.
Hope this is useful |:>)