Why won't my Apple Software Updater connect to Apple? Every morning, on one particular machine, I get a popup that iTunes has an update to install.  However, when I click download nothing happens.  If I try to use the Apple Software Updater manually it reports that the Apple Software Update Server cannot be found.  I have full Internet connectivity, having no problems getting to any other sites and my other machines on the network update iTunes just fine.  Any ideas?
I'd try downloading a full copy of iTunes rather than trying to update it: http://www.apple.com/itunes/download/