Take one of your Win2K pro machines which is in on your network. Install your ADSL modem and get it connected the internet. Once this is done enable internet connection sharing (ICS) on the pc with the modem installed, ('Sharing' tab in the properties for the internet connection).
Only problem you may have with ICS is it will reconfigure your LAN NIC with an addresses '196.168.0.1'. Also you will need to DCHP enable all the other pc's on the network as this pc will now act as a DHCP server and assign them all IP addresses within the 196.168.0.1->253
So, if you only have a small workgroup and have no worries about changing your IP address structure then this may be an option. To be fair you can change the address range ICS uses but that means a bit if registry editing.
Hope this helps
Cheers