Got mail working over on Dreamhost. Turns out the issue was that I needed to set the Mail Exchanger (MX) records on dyndns for the 3cats.us entry to point at the balanced mail servers (as opposed to a web server).

• mx1.balanced.spacey.mail.dreamhost.com
• mx2.balanced.spacey.mail.dreamhost.com

Hopefully those won’t change anytime soon as I don’t have an automated way to keep them up to date…

One other little note, the "hosts" file on Windows XP machines is located at c:windowssystem32driversetchosts