Autorun VB Code

Hello,

As a newbie some further help would be appreciated;
I have some VB code in module 1 that automatically inserts 'x' number of rows depending on value 'y'. What I could really do with having is a way of the code automatically running when a value is input in a given cell eg any row in column D.

The code for inserting new rows that I have used is;
[Code]
Sub ()
Dim Lst As Long
Dim Rw As Long
On Error Resume Next

Lst = Range("D" & Rows.Count).End(xlUp).Row
For Rw = Lst To 1 Step -1
With Range("D" & Rw)
.Offset(1).EntireRow.Resize(.Value - 1).Insert
.Offset(1, 1).Resize(.Value - 1) = .Offset(, 1).Value
End With
Next Rw
End Sub
/CODE

any help is really apreciated

thanks

Richard