If you have both Internet Explorer and Netscape Communictator installed, with IE as the default browser, and you no longer are presented with a choice when starting Netscape:
1. Make sure IE won't ask to be the default browser by clicking View / Internet Options / Programs
and unchecking Internet Explorer should check to see whether it is the default browser. Click OK.
2. Make sure that Netscape Communicator (or any of its' components) are NOT running.
3. Use Windows NT Explorer to browse to \Program Files\Netscape\Users\<Your Communicator Profile>.
4. Copy Prefs.js (or Prefs if Prefs.js does not exists) to Prefs.old.
5. Edit Prefs.js with notepad and locate user_pref("browser.wfe.ignore_def_check", true);.
6. Change true to false and Save and exit notepad.
7. Start Netscape Communicator and reply Yes to the dialog box asking if it should be the default browser.