Try changing the first sub to this: 
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)

Dim l As Long
Dim bEmail As Boolean

bEmail = False

If Not Intersect(Target, Sh.Range("C:C")) Is Nothing Then
    For l = 2 To Sh.Range("C" & Rows.Count).End(xlUp).Row
        If Not Sh.Range("C" & l) <= Sh.Range("D" & l) Then
            Sh.Range("C" & l).EntireRow.Hidden = True
        ElseIf Sh.Range("C" & l) <= Sh.Range("D" & l) Then
            bEmail = True
        End If
    Next l
    If bEmail = True Then Call SendEmail
    Sh.UsedRange.EntireRow.Hidden = False
End If

End Sub
Good training materials (but probably not samples) can be found here: http://www.excelforum.com/excel-prog...materials.html

Most (but not all) vba programs are fairly specific to their application. But if you read through the training material and ask questions on this forum I bet you can get through it. What you're asking for sounds pretty straight forward.