I got it to work at home last night.
On my main machine named Corona, I have a local drive E: shared as "Data E" with the rest of my machines.
On that drive I have the following layout:
E:\Audio
E:\Audio\Albums (Subdirs for artists and albums below this)
E:\Audio\Audible
E:\Audio\Podcasts
...
First I created a new directory to hold the shared library at E:\Audio\Library.
Then, I created a new mapped drive called M: and mapped it to \\Corona\Data E\Audio (bet you never tried mapping a drive network drive to a local drive before
).
Next, I opened MC and created a new library named Shared, cloning it from my default MC library, and saved it to M:\Library.
Finally, I opened the new Shared library, clicked on Audio, selected all files, and did a "Find and Replace..." of E:\Audio\Albums with M:\Albums in the Filename (path) field. Repeated for other directories under M:...
On my HTPC which is aptly named HTPC:
First, I created a new mapped drive called M: and mapped it to \\Corona\Data E\Audio. (sound familiar?)
Next, I started up MC and created a new library called Shared (no cloning) and saved it to M:\Library. (again sounds familiar doesn't it?)
Finally, I opened the new library, got the read-only warning, clicked OK, then started playing songs.
Now all it needs is a way to configure what fields can be modified from the clients (rating, playcounts, ...), instead of completely read-only, and it will be perfect!