Simon,

How many levels of sub-classing? Well, initially, just sub-class the base classes. That's easy enough. Basically, you'll want a class library that contains your sub-classed UI controls, like textbox, button, etc. Something like this:

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace MyCompany.WinUI.MyClasses
{
	public class MyComboBox : System.Windows.Forms.ComboBox
	{
		// code here
	}

	public class MyTextBox : System.Windows.Forms.TextBox
	{
		// code here
	}

	public class MyButton : System.Windows.Forms.Button
	{
		// code here
	}
}

~~Bonnie