I have designed a simple macro  to help you to identify all changes
that have done by another user  but you will need to follow certain
discipline. You need to duplicate your entire spread sheet  into
Sheet2 and to protect others for making changes in this Sheet2 you
have to password protect it and you will need to unprotect it
whenever you need to highlight changes in your original spread sheet
that has changes in it.

Sub Macro1()
'
' Macro created to highlight all changed values in an entire spread
sheet
' Macro created on 1/25/2006 by Mactikus
' Assign shortcut key Ctrl+Shift+C
'
RowNo = Cells.SpecialCells(xlCellTypeLastCell).Row
ColNo = Cells.SpecialCells(xlCellTypeLastCell).Column

For i = 1 To RowNo Step 1
For j = 1 To ColNo Step 1
Cells(i, j).Select
If Sheets("Sheet2").Cells(i, j).Value <> ActiveCell.Value Then
With Selection.Interior
.ColorIndex = 3
.Pattern = xlSolid
End With
Else
End If
Next j
Next i
End Sub

Run this macro on the spread sheet that you wish to highlight all
changes. All changes will be highlighted in Red. You can choose your
other favorite color if you wish.

I just joined this group recently and hope this macro can still
comes in time. Enjoy using this macro.