Searchable MultiColumn ComboBox

I wanted to implement a control on asp.net, such that the drop down list has multiple columns and also the user can type in the text and also has the facility to making dynamic suggestions for completing words as the user types.Please let me know how this can be done.
I know I can implement the multicolumn drop down using AJAX drop down extender control.
I need to know the typing in text box piece such that the drop down will make suggestions or any other alternative.Please suggest.