…not by me.
I finally found this entry in the Apple support forums, after going through tons of official suggestions for troubleshooting. This one worked like a charm, so I’m reproducing it here, in case anyone else is having the same problem (that is, that iTunes 8 would not install fully, or would work once but never again, or that the installer tried to run every time and prompted a reboot every time). The problem is in the shortcuts, folks.
Hunh....in a moment of curiosity, I went directly to the application in my Program Files (x86) folder and right clicked the .exe file > Run As Administrator and voila. Working iTunes. I then deleted all the different shortcuts I've been using and replaced them with new ones and I'm right as rain, at least for now. Apparently, shortcuts created by windows trigger this problem, including the one that automatically shows up in the start menu, and the one automatically placed on the desktop. Creating a shortcut manually yields no issues. Originally posted here
And it’s working like a charm, as he says, at least for now. What a clever chap.