You have a slow response time only between the computers? How is the response time to the Internet?
I doubt that the slow response time between your local computers is a result of your router. The number of ports simply defines the number of connections that can be directly/physically made to that device. Instead, since your network doesn't appear to have a WINS server or a local DNS server, I would bet that the slow response time (from one computer to the other) is due to the name resolution between the PC's that are connected. It appears that the only name resolution on your network is through NetBIOS.
There are a couple things you can try in hopes of making this process faster. The first thing you could try would be to access the computers by IP address rather than by computer name. This would completely bypass the name resolution step completely. For instance, say you are accessing a share on your other computer that is at the address 192.168.1.100. Rather than using \\computername\share you could try to use \\192.168.1.100\share
A second (more complicated) thing to try would be to add a LMHOSTS file. In Windows 2000 go to Start > Search > For Files or Folders... In the Search for files or folders named box type lmhosts.sam and hit enter. It should find the file in the C:\WINNT\system32\drivers\etc folder. Open this file with notepad and just read through it. It explains how the file is used. Once you read it and understand it you should build your own LMHOSTS file with the information pertaining to your own computers. The LMHOSTS file you create will probably only be 2 lines (one for each computer) and would look something like this...
192.168.1.100 computer1name
192.168.1.101 computer2name
...where the IP addresses are the IP addresses of the computers, and the computer1name and computer2name are the computer names that correspond to the IP addresses to the left. You could save that file as something like LMHOSTS.txt in the C:\WINNT directory.
Once you have your LMHOSTS file built and saved, you go to the Connection Properties (for your network card), then to Internet Protocol (TCP/IP) Properties, then to Advanced, and then to the WINS tab. Under the WINS tab, be sure the Enable LMHOSTS lookup is checked, then click the Import LMHOSTS... button and browse to the LMHOSTS file you created. In my example it would have been in the C:\WINNT directory. From there, keep hitting OK until you are out of all of those screens.
If you decide to use this LMHOSTS method, you should not use DHCP to automatically obtain your IP addresses, since your IP addresses could change and you'd have to update your LMHOSTS file.
One other thing is that you will need to do this LMHOSTS configuration on each computer (the 2000 and XP box) that is accessing a share on another computer.
I hope that helps. Let me know if you have any questions on any of that...
deeno