There shouldn't be any problem getting these babies to network in a workgroup without collisions. Fast Ethernet nics and a switch would be better, but you have enough gear.
First make sure that each NIC is not disabled in your hardware profiles. Then for each computer starting with the Win2k one, right click on my network places | choose properties | right click on local area connection | Properties | select tcp/ip | select "show icon in taskbar when connected and choose properties.
This is where you make static ip addresses for your network so all the computers will see each other. Some probably are right now, but some may be using a different subnet and may only be communication partially with NetB. Anyways I recommend Class C ip convention. So first machine to the fourth machine will be: 192.168.1.100 , 192.168.1.101, 192.168.1.102, 192.168.1.103 and so on as you add machines. You can go up to 192.168.1.254 with the third octet being one. MAKE sure that the subnet mask for all of the NIC's is 255.255.255.0
Don't set a default gateway, DNS servers or anything like that.
When you setup ICS you will probably have to enter the IP info for your Win2k box, but not sure. I used Winproxy on my home network and it was self configuring for the most part.
Now you should be able to play TCP/IP network games without any problems. As far as sharing resources between the computers, you will have to create shared drives, folders etc. and then map network drives from the other computers. You should be able to browse to the shared drives through Network Neighbourhood or My Network Places, then right click on them and select map network drive (select reconnect at logon check box if there, so the drive is always mapped when you boot up).
There's the basics in a nutshell. Good Luck.