Right-click the tab of the sheet you want, and select 'View Code.' This will open the Visual Basic Editor.
On the screen that comes up, paste the following code:
<font face=Tahoma><SPAN style="color:#00007F">Private</SPAN> <SPAN style="color:#00007F">Sub</SPAN> Worksheet_Change(<SPAN style="color:#00007F">ByVal</SPAN> Target <SPAN style="color:#00007F">As</SPAN> Range)
<SPAN style="color:#00007F">On</SPAN> <SPAN style="color:#00007F">Error</SPAN> <SPAN style="color:#00007F">GoTo</SPAN> myErr
Application.EnableEvents = <SPAN style="color:#00007F">False</SPAN>
<SPAN style="color:#00007F">If</SPAN> Target.Count > 1 <SPAN style="color:#00007F">Then</SPAN> Application.EnableEvents = True: <SPAN style="color:#00007F">Exit</SPAN> <SPAN style="color:#00007F">Sub</SPAN>
<SPAN style="color:#00007F">Select</SPAN> <SPAN style="color:#00007F">Case</SPAN> Target.Address
<SPAN style="color:#00007F">Case</SPAN> <SPAN style="color:#00007F">Is</SPAN> = "$A$1"
[C1].Select
<SPAN style="color:#00007F">Case</SPAN> <SPAN style="color:#00007F">Is</SPAN> = "$C$1"
[E5].Select
<SPAN style="color:#00007F">End</SPAN> Select
Application.EnableEvents = <SPAN style="color:#00007F">True</SPAN>
<SPAN style="color:#00007F">Exit</SPAN> <SPAN style="color:#00007F">Sub</SPAN>
myErr:
Application.EnableEvents = <SPAN style="color:#00007F">True</SPAN>
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">Sub</SPAN></FONT>
Hope it helps,