http://controlap.com/
BTW, there are others depending on what you are doing. You specified a W2k server, which low on my OS choises. You probably also don't want to run this on a machine you actually use on a day to day basis.
My preference for this type of setup (free) is NoCat (nocat.com) and for a pay hotspot is Mikrotik (
www.mikrotik.com). Put either on an isolated Pent I box and you're golden.