How can I filter options?

Hi, every one. I am now caught in a difficulty. I create a form to query the database. There are two 'select' items in the form. For example, I refer to the first 'select' item as $province and the second as $city. When I select a item of $province, I wish $city contains only the cities of the selected province. I think I should use the java script, but I don't know how to use it. Thanks in advance. -- ----------------------------- David Oilfield Tel:010-83557528-263 Mobile:13521805655 China Lottery Online Co. Ltd.