I don't know if this is how it works for others, but when I open a browser that is not my default, it always asks if I want to make it the default browser.
alright,...... in IE,..go to the Tools menu and select Internet Options. On the Programs tab,
there's a checkbox to have IE check to see if it's the default browser.
make sure this is checked, IE would then allow you to set it as your default the next time you start it and you should be given an option.