Problems with updating tables in SQL

Alright, here is my scenario. I have 3 tables in 2 databases I'm working with:

1st database is used to draw data from, it contains two tables:

First table contains employee information- the only columns I am using here are the Social Security Number and Employee Id.

Second table has address information/history. It is listed by employee number, and by effective date. The most recent effective date is their current address, past effective dates are they're past addresses. Also, they're address contains state, zip, etc columns.

2nd database is the database I'm trying to update periodically. It has a table containing both the most recent address, state, etc, and the employee's social security number.

(BTW, on a side note, I'm not responsible for the design of the databases, I'm trying to link the data through two different company's products for the company I am working for... very ugly).

Anyway- what I'm trying to do is get a table containing two columns- the employee's SSN, and they're most recent address/state/etc. I was wondering if someone could point me in the right direction?

Thanks,
Steve