Dynamic CodeList or Dropdown ListBox

Hi, experts.

     element Company:ID;

     element State:RegionCode;

     The State Dropdown List is showing all the regions. I don't want to  show every region. I just want to

     show particular regions for a particular country.

     I want to get a dynamic code list for RegionCode according to the Country of the Company that I type.

     Is that possible to do so?

     Please show me some way to make it happen.

Thanks,

May T.