Store Value-Listbox

Hi!
I want to display two values as two different columns in Dropdown list box but i want to store only one value in table.(Just like in Access).

There are two tables
1. Site (siteid, site_name)
2.Building(siteid,building_name).

There is 1:M relationship between Site and Building Table.

In my input screen there are two fields Sitename and Building Name .
I want sitename field which is A single Dropdown List box should be populated with siteid and site_name (from Site table) but when i select a value it should store only siteid which will be addes in Building table.Second field is building_name. All data will go in Building table. How i can modify the code (attached as txt file) to do this...


Thanks in Advance..