A Correction from CNET:
Last week we said installing the Microsoft Internet Explorer 7 beta 2 preview would render your machine unable to revert to an older version of IE.
That was a mistake. Users should be able to revert to their previous versions of IE by uninstalling IE 7 from the Add/Remove Programs panel.
If the Show Updates check box is selected, IE 7 beta 2 will appear under Windows XP - Software Updates and requires a restart after uninstall.