You only need to use an InputBox and put the code you have
inside a loop. In what follows the new lines are marked as such.

Sub insertrowswithformulas()
Dim iCt As Integer 'new
Dim iCt2 As Integer 'new
iCt2 = InputBox("Enter number of rows to duplicate.") 'new
For iCt = 1 To iCt2 'new
With ActiveCell
.EntireRow.Insert
Range(Cells(.Row - 2, "I"), Cells(.Row - 2, "AP")).Copy _
Cells(.Row - 1, "I")
Range(Cells(.Row - 2, "B"), Cells(.Row - 2, "G")).Copy _
Cells(.Row - 1, "B")
End With
Next iCt 'new
End Sub

HTH,
Merjet