This is the basic configuration screen for MacTCP.
Make sure the Obtain Address segment in the upper left corner is set to "Server". This way, all your IP addresses (like the Gateway address immediately below) are set automatically from Msen.
The IP Address section can be left alone- these settings come from Msen.
Be sure to set the Domain Name Server Information segment exactly as it appears here!! If this is not set correctly your internet applications (like Netscape) will not work correctly.
When you've completed this, click OK, then Restart your computer.
For more information about configuring MacTCP, you should check out Adam Engst's book The Internet Starter Kit for Macintosh. He goes into much more detail about configuring MacTCP than I do here.