Yary, > I have two uses in mind, one is trying out/debugging network scenarios, > the other is creating a virutal machine where a couple trusted users can > set up some network services (webserver, svn repository) separate from > my own. The first pretty much requires some kind of virutalization, and > the second is much easier with it, AFAIK. Take a look at http://sysjail.bsd.lv/ perhaps that suits your needs.
Cheerio, Chris