The bad news is, older macs with CPUs 68030 and earlier (such as the Performa6200CD that I have at home, circa 1995) cannot use the NSS described above, and can't run Open Transport. (Not sure what kind of CPU you have? Try looking up your model with GURU, a free software)
The good news! A wonderful person (Glenn Anderson) has written a patch that will fix MacTCP 2.0.6 so that it can again access the VT network. It takes a little effort to make it work. You have to have a fresh copy of the MacTCP control panel. If it's not fresh, you can edit it with ResEdit to freshen it up. I tried to patch a copy, copied straight from my system CD to a floppy, with no success. But I used ResEdit to clear the System Heap bits on the DRVR 22 resource and the ctrp 130 resource and then was able to run the patch. Want to do that? Get you a copy of ResEdit, open MacTCP, double-click the box that is called "ctrp." Under the Resource Menu, go to Get Resource Info, and uncheck the box next to the System Heap attribute. Do the same with the DRVR box. Now it should be ready to run the patch. Don't want to do all that? Here's a fresh copy of MacTCP 2.0.6 with the patch already applied. Download it, replace your existing MacTCP control panel with this one, RESTART YOUR MAC, and you should be good to go.