Filling a Combo Box with multiple Table Data

I want to be able to have multiple tables that fill my combo box. When I
click on one combo box I want the choice from that box to fill the table in
another box. Is there a way to look up the choice from the first box and
then use that to select the table and then fill the second box? This second
box would fill one field in the main table that I have. Right now I have
multiple links on the form that overlap each other and appear when a choice
is made in the original test box.

Any help is greatly appreciated. Please help the newbie.

Thanks