Well, if the tables can logically be linked using a SiteId, and one of the tables has a SiteName field, then you should be able to create a query which includes the SiteName field as one of the output fields. This query could then be used as the recordsource for a form ...
or ... perhaps in your old system, you used a combo box to view the SiteName of a site, as associated with the SiteId.
Its hard to second guess what you had before, but hopefully this will help,
Steve Lewy
Solutions Developer
steve@lewycomputing.com.au
(dont cut corners or you'll go round in circles)