Customizing Dialog Windows

I had to do this Export functionality that saves data in a file from the database after filtering by date. My first idea was "let's just export everything and only use an OpenFileDialog", but then the date filtering request came. I thought that changing the OpenFileDialog to add two date
time pickers would be an easy job, but, alas, it is close to impossible.

Good research came out of this, though:
FileDialogExtender - Customize a dialog by issuing API Messages to already open windows
Customize Your Open File Dialog - Customize a dialog by changing the registry
Advanced MessageBoxing with the C# MessageBoxIndirect Wrapper - a friendly C# wrapper class for the MessageBoxIndirect API that allows you to add a help button, custom icon, locale-aware buttons, and different modalities to a message box.
Control.WndProc Method - MSDN WndProc method