You can do both. Actually, you have to run a separate servers on different ports and then you can build virtual hosting based on that. There is
thread that describes vhosting using only one server but I guess it won't work for mixed ACS/OpenACS site.
Virtual server setup is described on this site:
http://downloads.hollyjerry.org/
I've also seen somewhere on the web an example of using Apache to serve as a proxy instead of nsvhr module (looked quite simple).
