Start by going here: http://www.theashergroup.com/tag/articles/nsvhr/virtual-hosting-howto.adp
That's the right way to start if off! :)

On the other hand, I'm also interested in the best ways of running multiple low-traffic sites on one machine. Right now it looks like it's 1 nsd per site minimum. But I've seen a server running Apache for hosted sites, and it seems to have less number of threads than the number of sites hosted. Any idea how they did it?