What you're doing is roundrobin DNS, i.e., you have two different IP addresses for your domain in DNS. This does not provide high-availability, because if one server goes down, and a user's PC gets the IP address of that server, he cannot reach your site.
If oyu want high-availability, you need a load balancer with a virtual IP address:
http://www.howtoforge.com/high-avail...at-debian-etch