The Virtual Hosting feature for Interaction provides virtual hosting features beyond the Multiple Sites support of Interaction. Specifically, it redirects requests for pages within a host to another URL path or web site.
In most cases, the integrated Multiple Sites support of Interaction supersedes the Virtual Hosting component. The exceptions are if you want to redirect a request to another site, or want to keep the various hosts as subfolders of the main site (as with conventional virtual hosting).
The Virtual Hosting component provides a dialog to configure hosts:

Interaction takes care of providing different documents depending on the host, even if the rest of the URL is the same. In addition, it allows multiple hosts to share the same forums and chat rooms.
Each host has an assosiated path that will be added to the URL before Interaction looks up the URL in the Locations. The locator of the locations of a specific site all starts with this path. For example, say that you have a host called "interaction.in-progress.com" with an associated path "interaction". A request for the URL http://interaction.in-progress.com/page1 will then map to the location "interaction/page1". Similarly, the homepage of the interaction.in-progress.com host would be the location "interaction/index" in Interaction.
If the path for a host is the URL for another server, the Virtual Hosting component will redirect the request to the corresponding location provided by the other server. This is useful in cases where a site has changed host/domain name.
The Virtual Hosts dialog is found on the Windows menu of Interaction. Remember to disable any other Virtual Hosting software when using the virtual hosting of Interaction.