We have a problem with some new customers failing to enter the proper state for their address. Apparently they don't enter a value for the state name that osCommerce can find in the zones database and therefore osCommerce returns an error message and a dropdown for the state with the state of Alabama being selected. Obviously the customers are not reading the error message and okay the "updated" address without noticing that the state they entered has been changed to Alabama.
To solve this problem I designed this modification so that osCommerce will display a dropdown list appropriate for each country, or a text input box if there are no zones defined for the selected country. As the country dropdown is changed so does the field for the state.