Why does Xcode 4.1 installation ask me to close iTunes when it isn't open? I am trying to install xcode 4.1 with lion. Apparently at 3/4 of the installation problem, it says to close itunes, which is not open. How can I fix the problem?
Use Activity Monitor, and locate the iTunes Helper process and kill it. As per an Apple support discussion and several other sources.

Update: The latest Xcode installer has been fixed and this should not be an issue now.