Nah... That's all old stuff. However, I would caution you... If you don't have a good, reliable, high-speed network you may have performance issues with the Library on the network drive. Even though I have a gigabit network, all my libraries are local (on C) and are synced to a network location.
However, that caution said... You can do it (and performance has improved since the old days).
Do this:
1. Find out exactly where (what folder) your Library is currently living. By default it is here: C:\Documents and Settings\<USERNAME>\Application Data\J River\Media Center 12\Library. YMMV, but you can check in the File --> Library Manager tool.
2. Close MC.
3. Find the above referenced folder using Windows Explorer (My Computer) and copy it to your NAS. So, if your NAS is mounted to the system via a network drive letter at M, copy the folder to M:\library\ or somesuchplace. Copy, don't move, for safety. UNC Paths work fine now, so \\nasbox\sharename\library\ would be fine too.
4. Reopen MC. Open the Library Manager.
5. Click Add to add a new library. Give it a name in the top box (something like NAS Library or somesuchthing). Hit browse and find the new folder on the NAS (or copypaste it into the box). Hit OK.
6. Double click the new entry in the Library Manager list to load it and make it the active library.
7. If all is good and right with the world, you can remove the old library entry from the library manager.
8. Rejoice and drink a beer.
9. Repeat 4 - 8 as needed for all other machines. If you have lots to do you may want to hold off on #8 till you're all done, for obvious reasons.