First make sure that regular Home Sharing (Preferences..Home Sharing) does not do what you're looking for, since that's the native, default way of sharing libraries with iTunes.
As Marcus said, shift-click lets you point to a library but it's a pain to use on a regular basis. If you're going this route, I recommend using junctions to create a reparse point from the default library location in /User/My Music/iTunes of each client towards the shared library location.
To avoid messing up file links within the library, just make sure to set the same music location in every client Preferences...Advanced BEFORE doing this, ideally a common mapped drive like "X:\Music". Even though the iTunes libray.itl contains the absolute paths of the music files, if the default location is different it won't add files correctly.
- In C:\Users\Me\Music\, move the iTunes folder to your shared drive.
In an elevated command prompt, create a link to your shared library folder.
mklink /D "C:\Users\Me\Music\iTunes" "X:\iTunes"
Now iTunes will open this library by default (X:\iTunes\iTunes Library.itl)
Note that the is not the location of the actual music files, but just the folder where iTunes will put the iTunes database files and downloaded artwork.
Finally, the main inconvenience outlined by the article bears repeating: assuming iTunes doesn't otherwise complain, having multiple opened instances of the same library will end up reverting changes endlessly, including play counts, ratings, and most importantly, any addition/deletion. Only the changes done in the last iTunes to save the file will actually be saved.
On the plus side, I can confirm that iTunes updates works pretty well. The first client to load the library will update it, and all is good for the next ones.
Best Answer
iTunes 12.10.11 for Windows (Windows 64 bit) should work wuth Windows 7. According to the same page: