prblm in populating checkboxlist with user name

Hi guys,
'i have to populate username in checkboxlist based on department selection in dropdownlist
kindly suggest how to acheive it.
here is table structure:
1>DEPARTMENTS1
DEPARTMENT_CODE    VARCHAR2(20 BYTE) DEPARTMENT_NAME    VARCHAR2(100 BYTE) ID    NUMBER(11,0)
2>OFFICES
OFFICE_CODE    VARCHAR2(20 BYTE) OFFICE_NAME    VARCHAR2(70 BYTE) CURRENT_DIARY_NO    VARCHAR2(50 BYTE) FIRST_OFFICE    VARCHAR2(20 BYTE) SECOND_OFFICE    VARCHAR2(20 BYTE) THIRD_OFFICE    VARCHAR2(20 BYTE) FOURTH_OFFICE    VARCHAR2(20 BYTE) FIFTH_OFFICE    VARCHAR2(20 BYTE) SIXTH_OFFICE    VARCHAR2(20 BYTE) SEVENTH_OFFICE    VAR ...