Go to Control Panel and double click Add or Remove Programs. You should see
Internet Explorer 8 Beta listed. Hit the Remove key.
Note: If you've installed any updates or programs since installing the IE8 Beta,
you may be asked if you want to continue the uninstall. If you click Yes, you
might want to reinstall the programs and visit Windows Update/Microsoft Update
after the uninstall process is completed.
You'll be asked to restart your computer. When your computer restarts, IE7
should be restored if it was the previously installed version.