A required component cannot be installed when you try to install the Zune software:
http://support.microsoft.com/kb/944938?sd=zune
Okay so don't try to update the software right before you get on a plane..... when it failed it was a sign from the Patching Gods not to do it....
Read the complete post at http://msmvps.com/blogs/bradley/archive/2008/05/07/some-things-you-should-just-not-tempt-fate.aspx