how to populate lov using record group

[lucky]

i want to restrict lov by using record group.for example i have a form that contains two fields deptno,dname in tabular form.and i have a button on form that displays lov.first time when i press buton then all deptno will be displayed.when i select one of them,then for second time that deptno that i have seleced first time should not appear in lov again.
i mean to say that all deptno that are selected from lov will not appear again in lov.
please give me code example if anyone have that.
and tell me how to use it.