Hi, you can capture the SelectionChange event, or double click, or
many other application events. See the code below that would be placed
inside the appropriate Worksheet Code Module. The 'Target' parameter
is a range variable that is set to the cell that was selected. You can
use 'Target' to test the cell address, row, column, etc... or even use
it change the value and more.

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Column = 1 Then
Call updateMacro
ElseIf Target.Column = 2 Then
frmEnterTime.Show
End If
End Sub

See Chip Pearson's site below to learn more about events:
http://www.cpearson.com/excel/Events.aspx

HTH—Lonnie