A form plug-in needed with parent-child combo boxes

Hi all,

I need to collect address data from people via a form. They will select data from three combo-boxes which shows country, city and district lists.

Each combo-box will filter the next one. When user select a country, he’ll see only the selected country’s cities, and when he select a city, he’ll see only selected city’s districts. If a country is not selected, he won’t see cities and districts, and if a city is not selected, he won’t see districts.

How can I do this easily? Do you know a useful plugin for my need? Any help would be appreciated.

Regards.