Multiple domains

Hi everybody. I've seen many examples on setting up DNS for ONE domain but where are the examples for a setup where you have more than one? Please help out. Our server (OSX 10.1.4) handles mail, ftp, www in a NAT environment. Now i'm thinking of setting up DNS on this same server so that our users won't have to use the internal IP-number, 192.168.90.2, every time they go to our webpage etc. Our ISP has primary and secondary for our domains for the rest of the world. We have 3 domains: company1.se, company2.se and company3.se. They all have aliases for: www, ftp, and mail. Company1.se also have a subdomain called project.company1.se. The server's hostname is: server and has the static IP address 192.168.90.2. It's got Bind 8 on it. TIA Thomas Ericsson