Endless Redirection of Drupal on IIS
Need more info! The Devel module has an option for interrupting page redirection and displaying the page you're about to be forwarded to - very handy for debugging redirection. Common redirection issues stem from Rules, Context, Delta, and even just the URL Alias system within Drupal itself.

The transition from Apache to IIS is an interesting hint though - any chance we can take a look at your .htaccess and web.config files to check for differences? Something else to watch for could be trailing slashes and the difference in server handling, as well as the user that PHP is running as under a possibly different CGI.