EXCEL VBA Question

Dear Experts,

In Excel97, I want a Calendar to pop-up when the user clicks on a cell in specific cell ranges. The user should only be able to enter dates chosen from the Calendar into the cell.

At the moment, I am using the following code. Form1 has the Calendar control on it. What this code does is that when an Active Cell is within the specified range, then when the user presses a shortcut, it runs the macro to pop-up the Calendar. This works fine, but I'd like the Calendar to pop-up when the user simply highlights a cell (makes a cell Active) in the specified ranges.

Thanks,
DocNash


Sub auto_open()
Dim KeyCells As String
KeyCells = "D3:D1000, E3:E1000, H3:H1000, J3:J1000, K3:K1000"
If Not Application.Intersect(ActiveCell, Range(KeyCells)) Is Nothing Then DoIt
End Sub

Sub DoIt()
UserForm1.Show
End Sub