Setting this up is a two stage operation. Firstly, you need to configure your machine to accept connections on multiple ip-addresses. This is vendor dependant, and you should consult the machine documentation on how todo this, although there is an extremely good compendium of such information here.
Once you have the machine configured correctly, then the second stage is to setup Zeus Server with multiple virtual servers. Create the first server as you would normally, but in the advanced configuration section, edit both the IP Bind Address and IP Name to the values you require.
Then choose the Create a new virtual server option off the Server configuration page. Again edit the IP Bind Address and IP Name on the advanced configuration page, and you may also want to set a different database to be used for this virtual server, which can be specified from the database configuration menu.
At this point you should be able to start the server, and you will get a list of two virtual servers that have been started. Check to see that these both work correctly, then add more virtual servers using the same method as required.
There is no limit to the number of virtual servers a single copy of Zeus Server can run, apart from OS limits on the number of file descriptors given to a process.