populating 3rdListbox with 2 other listsBOxes with multiple selections

[Dotnetdeveloper06]

HI I have 3 listboxes in which 3rd listbox has to be populated depending upon selections in first 2 listboxes.My first 2 lists boxes are multiple selections.so if i select 2 elements in first one and 2 in second listbox . i need to make 2*2 combination. i know i can do by taking both of them in 2 arrays and get the vaules for 3rd one. but i need to populate the 3rd listbox when selection in 2nd listbox is made.so for every selection in 2nd listbox i need to compare with selected items in the first one and store them in temp table(by adding rows for every selection)and when all selections in 2nd one is made. i need to populate 3rd one with temp table. Hope you ppl got my idea. i need coding help with this part. i tried coding but wats happening is everytime only latest selected vaules are visible not all the prevoius ones. So can anyone help me. i know its very easy but i m very confused. Thanks,in Advance.Please help me. Dotnetdeveloper