ADO and querying an union

hi, i'm using MS Access 2002, and have a number of tables having the same
field for some important serial numbers. i have these tables linked up with
an union query. but for input, i have a form. right now, i want to be able to
click a button on the form and check whether the serial i have entered is
unique. it SHOULD be going to the query and checking the entire updated list
from all the tables. but i don't have any idea of connecting ADO to a query
instead of a table in VBA...T.T

is there anyone who can give me some pointers??
.