Hello Sasidhar
Yes you can sort the List box(selectbox) ,for that you will have to create object ,since in order to sort the Text of List box ,you must have to arrange their values in the proper order.
So it's best choice to create object and do the sorting .

You can use array.sort() method only to sort array elements,since List Box may have different value and text ,so you will have use Custom Object .

Hope You will get the answer.
Cheers :)

vinod