Interestingly, Apple doesn't provide the new AirPort Utility as a download since it's provided on the installation CD that comes with the new 802.11n AirPort Extreme Base Station. Have you tried contacting Apple for a replacement CD?
As an option, here's a workaround...
o Download a copy of the
Less_MSIerables utility to the Windows Vista desktop, and then, extract it to a folder of your choice.
o Download
AirPort Base Station Update 2007-002 for Windows to the Windows Vista desktop.
o Use a program like winrar or winzip to uncompress that file to a new folder
o Next go to the folder in which you extracted Less_MSIerables.
o In a subfolder you will see a file called lessmsi.
o Right-click on this file, and then, click "Properties."
o Click on the "Compatibility" tab.
o Enable the option "Run this program in compatibility mode for: Windows XP (Service Pack 2)."
o Click "Apply," and then on "OK."
o Right-click on the lessmsi file again.
o Choose "Run as administrator," and then, after the program starts click on the "..." button to browse to the folder where you unzipped AirPort521Update.
o Select "APSetup," and then, click "Open."
o Select "APUtil.exe," and then, click "Extract" to extract the file to the Vista desktop.
o A file folder will appear with a name like
cab#APSetup.cab1.
o Open that file folder and you will see a file named: APUtil.exe.
o Either run APUtil.exe from it's present location, or copy it to its final destination.
