what makes it "Server"?
Some of the most notible differences are:
- IIS in server allows you to create multiple websites, ftp sites, and virtual smtp servers - whereas w2k pro just lets you create 1 website.
- It comes with the DNS service which lets you run your own dns server.
- Like Tony said, it comes with Terminal Services in remote administration mode that will allow in addition to the console session up to 2 concurrent terminal service connections (or remote desktop connections) by default.
- It comes with the routing and remote access service for setting up VPNs, etc.
- It comes with a telnet server, snmp service, and other things that make it more server like.
- It's required if you want to run SQL server 2000 Standard or Enterprise.
Those are just off the top of my head - so that list is by no means all-inclusive. Just most of the biggies.
- trs