As described in Tech Tip 00-228, if you find that launching 4th Dimension causes your system to initiate a dial-up connection to the Internet (i.e. your modem dials out), you can remove the TCP/IP Network Component from 4D to stop this from happening.
However, here is another alternative. If you are willing to do without the convenience of automatically connecting to the internet whenever a TCP/IP application is run, you can set the dial-up connection properties to force the operating system to ask for permission before initiating the PPP link. This way you will have to manually connect to the Internet before using your web browser, e-mail, ftp or news client. But neither will 4D be able to initiate a connection to the Internet without having to surgically remove its TCP/IP Network Component.
For details on configuring Windows 95/98/NT see section "To change the properties for a Dial-Up Networking connection" in the Windows Help files.
For details on configuring Mac OS 8/9 see section "Setting up Remote Access" in the Mac OS Help files.