Q: "There is a problem with this Windows Installer package ..." error messages when installing iTunes for Windows 7 64bit

I was promted to upgrade to the new itunes version today (11.0.2.26), but wish I never had as the previous version worked just fine!! I have been unable to install the new version and keep getting the message about there being a problem with the Windows Installer package. I tried following the instructions on this support pages on removing all Apple programs but that didn't work either!! I have Windows 7 64 bit and am close to throwing my PC out of the window!! Quicktime will not re-install correctly either...

Any suggestions will be most gratefully received