That is odd, I checked that key and it is not even locked on my computer running UAC enabled! What you could try if you want to is to restart and right before your screen says "booting windows" and it has the animated screen press "F8" and select "Last known Good Configuration that Worked". That will restore your registry to an older point where maybe you can install itunes again. If it does not help try a registry cleaner, if that still does not help then it looks like you are in hot water dude.
Have you installed and deleted one to many software programs lately? You may have to run your Win 7 installation disk to repair your registry.