3 table update query

Hi,

I am trying to figure out how to update a couple of thousand logon names based on the following two database, three table structure:

(database, table, columns)
database 1, table 1: id, newlogon
database 1, table 2: oldlogon -- I need to update this field
database 2, table 1: id, oldlogon

the relation is between database 1 table 1.id and database 2 table 1.id...

based on these three tables how can I update database 1, table 2 to contain the newlogin from database 1, table 1?

any help really appreciated!