How to replace a drop down list with a combo box

I am developing a Web application (ASP.NET using VB.NET). I have a drop down list in my form. However, I would like to replace the drop down list with a combo box to provide more funtionality. In Web forms, how I should go about doing it?
A drop down list IS a combobox in ASP.NET terminology. What functionality do you need that is missing?

This was first published in October 2004