Got those MacTCP 2.0.6 Updater Blues? Many MacTCP 2.0.4 users have had bad experiences trying to use the MacTCP 2.0.6 updater (see TidBITS-255). Specifically, the updater application often refuses to update the existing version of MacTCP because the driver resource ".ipp" doesn't match what the updater expects.
The updater works properly on a "clean" copy of MacTCP 2.0.x that's never been installed; however, if you're absolutely stuck without a "clean" copy, this particular problem may be fixed with ResEdit (but no guarantees):
1) Make a copy of the MacTCP 2.0.x control panel.
2) Using ResEdit 2.1.1 or higher, open your copy of the MacTCP control panel.
3) Locate the DRVR resource and open it. You should see only one resource, ID 22, called Driver: ".ipp".
4) Select the driver resource and choose Get Resource Info from the Resource menu.
5) At the bottom of the resource info window are six checkboxes: uncheck the System Heap checkbox.
6) Save your changes and quit ResEdit.
7) Run the appropriate MacTCP updater on your modified copy of the MacTCP control panel.
8) Swap the updated MacTCP and the old MacTCP in your Control Panels folder and restart.
Note that updates to MacTCP 2.0.4 or 2.0.6 cannot be performed on versions 1.x of MacTCP. [GD]