How about something like this (you need to copy this into the Workbook
module).
Regards,
KL

'--------------Code Start--------------
Const Password = "" '<=Your password here if any

Private Sub Workbook_SheetSelectionChange(ByVal Sh As Object, _
ByVal Target As Range)
'Prevent multicell selections.
If Target.Count 1 Then ActiveCell.Select
ActiveSheet.Unprotect Password
If IsEmpty(ActiveCell) Then
ActiveCell.Locked = False
Else
ActiveCell.Locked = True
End If
ActiveSheet.Protect Password
End Sub

'--------------Code Finish--------------

"newbie" wrote in message
...
Is it possible to protect a cell if the value is not equal to zero or
blank?

I am using Excel 2002 and want to allow people to be able to enter values
into the worksheet, but once they have been entered, I do not want them to
be
changed.

Thanks,