James,
there are various virtual hosting options. For AOLserver 3.x I recommend nsvhr/nsunix available from http://sourceforge.net/cvs/?group_id=3152
Browse the AOLserver CVS tree http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/aolserver/ and you'll find the documentation (which is included with the modules).
Search the OpenACS site for 'virutal hosting' to get answers to most questions relating to virtual hosting as well as other virtual hosting options.
/Bart
