I use a datacombo box, fill it using ADO (DataEnvironment Addon)ie Select 'Data Environment' under Project/Components/Designer. By playing with the combo box properties...

Style = 2. Dropdown list
MatchEntry = 1. Entended Matching

...it does what you want to do. However, have never tried doing this with normal combo box and DAO. (Not sure if you can)

Good Luck