I am assuming that both databases are on the same SQL Server instance. If you want to transfer a table between databases, try using DTS if you are on SQL 2000. There should be a method for transferring database objects. I won't explain how to use DTS so you will have to go to Microsoft's website or Books Online.
Another method is to manually create a T-SQL script of the table structure. Run it against the other database and perform an insert command with the values being pulled in by a sub query.
INSERT INTO <databaseB>..<tableA>
SELECT * FROM <databaseA>..<tableA>
Make sure to replace the examples <...> with the actual DB objects. Also for this script to work, both tables must have the exact table structure.
I woudn't recommend using the SELECT INTO method which will create a table and SQL will guess what the data types are and you will have to manually add the constraints back.