Hi Mike, I'm not sure exactly what you are asking either so let me say what I think you are asking.
You have mikeshome.org setup for email and are running postfix on your linode to handle it. You want this same postfix install to handle mail for someotherdomain.com as well.
The answer is you just need to point the MX record for someotherdomain.com to mikeshome.org. Something like:
someotherdomain.com. 14400 IN MX 0 mikeshome.org.
Thats all, its just that easy. The harder part is setting up postfix to properly handle all of this new mail. You also might find my DNS Check tool helpful:
http://www.nabber.org/projects/dnscheck/
Neil