The Default browser, is the one set up to handle URL:Hypertext
Transfer Protocol. Netscape looks specifically at the Application
entry in the DDE section of the File Types dialog.
Registry Key:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\HTTP\Shell\Open\ddeexec\Application
Open Netscape:
Go to Edit | Preferences | Advanced | System
Under Protocols
Enable: http: and https:
Under File Types
Enable: HTML
Go to Edit | Preferences | Navigator
Click on the "Set Default Browser" button
Close Netscape
Go to Start | Settings | Control Panel | Internet Options
Click on the Programs Tab
Disable: Internet Explorer should check to see whether it is the default browser
NOTE:
It is sometimes necessary to make Internet Explorer the default browser, first.
Go to Start | Settings | Control Panel | Internet Options
Click on the Programs Tab
Enable: Internet Explorer should check to see whether it is
the default browser.
For Windows 2000 SP3 and SP4, and Windows XP SP1+ Users:
Microsoft released code that is added to Mozilla, and Netscape, that allows it to be controlled via this utility. This utility will work with Netscape 7.x, or Mozilla 1.3+. Note that the utlility is only included in Windows 2000 SP3, and SP4, and Windows XP SP1+. If the shortcut for this utility has inadvertently been removed from the Start Menu, it can be accessed via the Add/Remove Programs section of the Control Panel.

Windows XP

Thanks to MinnesotaMike for the Windows XP Screen Shot.