How long is "long"?

Do you really need isolation?

As for cable, I always use UTP cable. It is twisted and has characteristic impedance very close to 120 ohms.

If you don't have a copy of the Serial Port Complete by Jan Axelson, you must get it soon.

Lastly for short distances and low baud rate (less than 9600), termination is not really necessary.

Ioannis