How can I tell if I have the 64-bit version of iTunes installed?
On OS X, you can open iTunes and go to iTunes -> About iTunes and it will tell you. On Windows, you can get to the same dialogue by going to ? -> Info, it won't tell you though. You can open the task manager and if there is a *32 behind the process name, it is 32 bit.

It looks like the Installer is 64 bit but the application remains 32 bit on Windows.