title: How to perform textbox and dropdownlist in one control?
body: <p>For example : I have UserID and UserName. So I use DropDownList. UserName is DataTextField
  and UserID is DataValueField. So User can choose their name and I save UserID to my database.
  But If User is new and not registered. I want to allow to type in DropDownList and I save the name to database. So for registered people can choose and not registered people can key in.</p>
  
  <p>How should I do? Can anybody give me suggestions?
  Thanks</p>