You didn't state what operating system or browser you are or want to use but, I am assuming your using WIN XP and IE 6. But, even if your using Win 2000 or ME (I am not sure about Win 98), you should be able to go to your start button and click on "Set Program Access and Default." If you don't find it there, open up your Control Panel, click on "Add/Remove Programs" and on the left side of the panel you should find the Windows icon saying "Add/Remove Programs." Click on that.
(1)Click on the downward pointing double arrows on the right side of the box. When it opens, the top line should tell you what browser you are using. Click on the same arrows (now pointing upwards) to close it.
(2)Move your pointer down to the double arrows on right, next to "Custom" and click on that. You can then make the necessary changes to get the browser back that you want to use as your primary.