One of the above suggestions worked for me. As stated above:
When using Vista 64 bit, you have to use the 64 bit version of IE to visit the Apple iTunes site.
1) From the start menu, chhose Run...
1) In the Run dialog box enter the following into the "Open" field:
+C:\Program Files\Internet Explorer\iexplore.exe+
2) In the new Internet Explorer window, visit the following web address:
+
http://www.apple.com/itunes/download+
You'll then be offered the proper iTunes64Setup.exe installer option.