How many domains can be put in 1 server?

Hi, I am setting up a window 2k domain in our company network. I have installed DNS and Domain Controller on a same machine(ex. ABC.com). It works great until I try to add another domain (123.com)using same machine. The DC just wont show 123.com in its directory even though I set up a new zone (123.com) in the DNS section. So my question is, can a machine (a win2k server set up as a domain controller ) act as domain controller for two different domains (abc.com and 123.com)? or you have to have seperate machines act as DC for each domain.

Any answers are appreciated.
Thanks