Open Excel File in Internet Explorer
 

I currently have Windows XP SP2 with IE 6 and have upgraded to Office 2007.
Since the upgrade, reports that used to open within Internet Explorer (Excel
reports in .cgi format) now come up with a message stating that the format of
the rerpot is different and it asks me if I still want to open it. I click
"Yes" and it opens the report within Excel now instead of Internet Explorer.

How do I stop the warning about the .cgi file and allow it to open in
Internet Explorer like it used to?