Triggering an event from a cell

Hi, is there a way that I can get my spreadsheet to trigger and event after a particular cell is updated?

Brilliant, thanks for your help

I now have another problem - I'm trying to get it so that when a value is entered in one cell it appears in another. However, I want it so the next time a value is entered in the first cell it adds it to the value in the second cell. The code I have tried (which is wrong) is the following:

Private Sub Worksheet_Change(ByVal Target As Range)
c3 = cells("c3").Value
d3 = cells("d3").Value
If Target.Address = "$d$3" Then
c3 = cd + d3
End If
End Sub

Can anybody tell me where I'm going wrong?