One drawback to the "use DNS" approach is that machines that aren't in DNS or uncorrectly configured wont be detected. I can imagine if I were doing this I might try to cycle through possible IP addresses and use ping. I could write the thing I am talking about in about 15 minutes. It would be embarassingly crappy, yet functional. (that is why i yam heer). If you ask me nice enough I could probably get talked into it.