Combobox Hell

Question

 Hi All,

I have ap problem related to database and combobox..
i have a combo box which retrives the number of UserID from Database as
1
2
3
4
5
6
7
8
Now what i need to do is , if i select 3 from Combobox, then Userid1 ,Userid2, UserID3,
Should get selected and if 2 then Userid1 and userId2 Sholuld get selected from database...
Its very urgent...plz...help :(
Thanks in advance