Ok, I am not familiar with 2K but hasnt that got its own network wizard ?
When you run the network wizard on your main pc select the option This computer connects directly to the internet and other pcs connect through this pc.
Select File and Printer Sharing if required.
Just close the wizard at the end.
Run the network wizard on 2K ( it must have one as even ME had its own).
Select the option, This computer connects to the internet through a residential gateway or other computer.
Select File and Printer Sharing if required.
Make sure that both the laptop and the pc have the same workgroup name, usually MSHOME.
Check that you can see both pcs in View Network Computers from each pc.
If you cant see both then temporarily disable the firewalls on both pcs.
If you can then see them you need to configure the firewall for ICS and/or file sharing.