One of the biggest differences is that you have multiple 'primary' domain controllers with fail-over capability. So if you have two co-equal PDC's each with their own (compatible) DHCP ranges then the AD rules & user logons capability are safely maintained should one of your servers fail. That way after you rebuild the failed server you can replicate your AD back to it without having to rebuild all your user rules etcetera.

There's also some neat DFS (Distributed File System) tricks you can use so that you can move your shared files around without having to re-map things on all your clinets (so long as the mapping calls \\domain\DFS-Share instead of \\machine\share).

W2k server is a huge improvement over NT4 especially wrt sensable user administration. There are a few new concepts to get your arms around (hence the book recomendation) but I think you'll like it much more, especially for those W2k clients (adding printers takes about 10 seconds). Also W2k server can hold print drivers for downlevel M$ OS's.

-Zeke
/edit: man Drakino, you're too fast for me...