sounds like you are talking about 'cascading comboboxes'. There are a number of solutions - try googling 'cascading comboboxes' to find out more. A common solution is to have the rowsource of your second combo to be something like this
Code:
SELECT *
FROM myTable
WHERE afield=[combobox1]
in the rowsource (as code, not as a query)
and in the combobox1 afterupdate event put
combobox2.requery
if it is not just a matter of changing the criteria then in the combobox1 afterupdate event put something like
Code:
select case combobox1
case 1
combobox2.rowsource="SELECT * FROM table1"
case 2
combobox2.rowsource="SELECT * FROM table2"
end select