I am also looking into this, as I just dabble in sysadmin stuff, so this might help you...
I have heard that Virtual IPs are a good route to take, so whichever server boots first will be the primary server, and the next to boot will be secondary. If primary goes down, I am assuming secondary server will assume it is the primary.
I think this is how it works, but I am not sure, so don't quote me... just typing my thoughts really...
Primary server: 10.156.23.1
Secondary server: 10.156.23.2
Setup a virtual IP on both for 10.156.23.10
and have your router port forward to 10.156.23.10
Like I said, I **think** thats how it works, and I'll give it a try next week. If anyone else has any ideas or corrections to my theory, please let me know