SSH on port 443

You would have to modify /etc/sshd_config

I don't know that it can run on 2 ports, I've never tried that, but it might work. If the system is behind a router, you can use the router and map from port 22 to ports 22 and 443.

I know from when I was changing SSH ports in Tiger days it wasn't JUST sshd_config that you had to edit. You also had to edit the prefs for launchd as that is what actually listens to the ports and launches the appropriate applications. Follow the hint below:

http://www.macosxhints.com/article.php?story=20050707140439980

I'm not sure if things have changed in Leopard, but I'm pretty sure they haven't.

Also, if you're behind a NAT router, then you don't have to change any settings on the computer, and can simply do port mapping on the router.