This article is excellent for those looking to find ways to track rogue hosts on a network. The article describes how to do this the same way that I show Jr. Security Admins to perform the task, so I can assure you that it is a good read. It also has several links to look up MAC addresses and see what manufacturer is associated with them. This article also deals with rogue WAPS and DHCP servers.

http://www.securityfocus.com/infocus/1705

--TH13