Microsoft is trying to faze out the nightmare that is WINS with windows 2000, but it cant quite do it. Thats because it is still needed in a heterogenous network of NT4 and Win2k machines. If you have a Win2k network only, with AD, then you can (and should) use just DNS.
Its kind of a shame though, since the version of WINS that comes with win2k server is the best yet. A vast improvement over NT4