Alright, so then you should have installed the package BIND as part of that process.
Did you set up a DNS Zone for your domain in the ISPConfig control panel? Did you also register your name server with your domain registrar as the authoritative name server for the domain? Without the latter in particular, the internet at large won't know to use your server for DNS lookups on your domain at all.
See this HowTo:http://www.howtoforge.com/how-to-run...and-fast-hosts
The last section (about Fast Hosts) will be different based on who your domain registrar is, but the basics are still the same - you need to register your name server with your registrar before everyone will know where to look.
And as I said in the previous post, there is no need to run two servers at this time. Just create two name server DNS names pointing to the same IP address and it will work fine.