Just for some clarification...
Is it just one field that needs to be transferred over, or could it be whole table. It it is a whole table, you may want to consider having one database hold the table, and then creating a link to that table from the other database.
If it is just one field, are there any other fields in the tables that match and could be used as a reference when updating the field in question?
Let us know, there are probably a whole handful of people on this forum that could help you out.