This can happen when the Airport Utility installation download can't find an authentication file - short of doing a clean install of Windows 7, try the following:
1. Delete any old Windows folders if Windows 7 was an upgrade
2. Turn off anti-virus programs
3. Turn off the Windows Firewall
4. Delete any partial installations of the AU that may be present
If the above does not work then try to download the previous version of the AU 5.5.3 at http://support.apple.com/kb/DL1391
My problem solved.... When I right-clicked Airport Utility and checked under Properties/Compatability Mode, The compatability mode box was checked & was set to Windows 7. This may have precluded it from running under Windows 7 SP1. When I unchecked the box everything was fine. Thanks...hope this helps someone else...