adding items in a table whose contents are displayed in a combo box

Question

I have a combo box which displays the values of a table "city(cityid, city name)"...
city id is the value member and city name is the display member..
Now i have to add the city name in table through combobox...
This will be done by the user!!!
I'm not able to do this, if anybody could help?????
Pls.......