If you're using mysql you can select across databases by specifying their names before the table do this:
SELECT * FROM db1.acct, db2.acct_data WHERE acct.id = acct_data.acct_id
Where your tables look like this:
database db1:
table acct:
id INT
(other data)
database db2:
table acct_data:
acct_id INT
(other data)