I found this to be easy, but I am not sure it's a standard way of doing it: I use godaddy for domain names and forward those to specific ports on the server. I also have MAMP Pro installed on the mini that handles mysql and all that gorp. Then under Server / Web Server I've identified where all the websites are, and which port they belong to. Seems to work great! Cheers,
Are you using Mac OS X Server?
If so, this is trivial - just use Server.app to create a new Site (Server.app -> Web -> + button).
In the new site's configuration, enter the hostname that maps to this site.
Rinse, repeat for as many sites you require. Apache will look to the hostname of the incoming request to work out which site configuration to use.