If you're starting from scratch, which I would advise, follow this guide:
I tried the other distros but debian lenny worked the best.
Then you need to set the name servers up:
These tutorials are for ISPConfig 2, but they should give you the idea:
Leave it 72 hours for the nameservices to settle.
Then use the DNS templates to make dns zone entries for your sites. (Remember when it asks for an IP it's the public ip not your lan ip)
Assuminng you've done port forwarding from your router It should then work straight out the box.. Click sites, create site and away you go.