how to handle ID and dispaly value for a coloumn

Hi,

I wanted to know how to handle ID and display value for a coloumn in APEX page?

e.g. I want to create an Apex page to create employee records, so I will be creating Form type page with fields "first name", "last name", "grade", "department".

first three fields are free-form text for user to enter any value where as the fourth field is "popup LOV" type item when selected showing list of departments i.e. "department ID" and "department name".

my question is how to show the "department name" on the page but internally save the "department ID" into employees table?