I run Bootcamp on my Macbook and want to be able to run iTunes in both OS X and Windows 7 with the same library. I don't just mean having access to my mp3 files on both OSes, I mean things like ratings, play counts, playlists, etc. will be the same. Can I do this?
This solution may very well not be to your taste, but the simplest thing I can think of that doesn't involve the phrases "disk partitioning" or "file permissions" would be to sign up for iTunes Match and match / upload your music collection, thereby making your music available to both your Windows and OS X partitions as though they were simply different devices (which, for all normal intents and purposes, they are).
I recognize the downsides to this approach:
But the result is a fairly painless and reliable solution, which does indeed keep your playlists, rating, and play counts in sync.
Store the library files on an external drive.
In your iTunes preferences you can select the storage location. Set it to the location on the external drive both on Windows and OS X.
Preferences and some other settings, as well as caches will not be accessible on both OSes, but that data that is important, like movies/music/apps/books etc. will be accessible. This way you won't have to download and store all of your purchases twice.
Another positive outcome to this is that you can always take the drive and connect it to another system and all of your purchases will become available there. Just don't forget to add the library in the preferences.