Why Not I.E.??
I have come across this problem where IE would not set as default browser even after the option “Internet Explorer should check to see whether it is the default browser” from Tools > Internet Options > Programs is turned ON. This happen after installing Avant browser.
So, if you should experience the same, just issue this command from RUN box or your command prompt: “shmgrate.exe OCInstallReinstallIE”
Your I.E. 6 should be set as default browser. But just remember that this fix only works on Windows XP with SP1 or later only.