Refresh only one dropdown box on a page

[tjbarr]

I have a form with many fields and a drop down box called fruit. Lets say it has three choices:
apple
orange
banana.

If the choice is not on the drop down box e.g. grapes the user clicks a link to a new table called add_fruit to add the new fruit and details about the fruit. On submit I want to close the add_fruit table and go back to my original form - refresh only the dropdown box "fruit" - so now the user can pick grapes.
How can I do this?

[Roger_Ramjet]

AJAX: personally I recommend Prototype

With this you can display the add friut form, send to db, return new details and update the drop down all without a full page load.

[tjbarr]

Do you have an example?