Parameter passing for query through form.

[Joe]

I have a form that brings up a list of companies and
contacts within those companies and via double click,
associates a contact to a different record.

Based on the number of companies and contacts, I would
like to provide a selection mechanism to limit the
listing from. ie allow a user to select the "A" box and
the seleciton list would only show companies whose name
start with the letter A.

I would like to use some sort of parameter passing as
oppsosed to creating 28 different queries, but am having
problems being able to create a universal query that
accepts parameters..

Any and all help would be much appreceated..

best,
J.