For e.g: a set of data:

UB UC
1 23
2 444
3 1
4


I have created a drop down list allowing me to select heading UB, UC.
I need another drop list that will allow me the select the values under
those headings, and the values on this list should depend on which heading i
select...i.e. If i select UB in the first drop list, the values under UB
should appear on the second drop list.

Anyone knows how to make that happen??