great advice J.

If you are looking for low overhead and low cost I suggest Freebsd on moderate server or high end commodity hardware (amd64 support is stellar on freebsd) and using samba. To my understanding with samba file attributes between the 4.2bsd FS and the clients are abstracted nicely. Netapp uses BSD as its core OS, for instance. If you are looking for a cheap appliance, check out Snap fileservers. We have them at work and, like anything else, they can be configured in a good way or a bad way, but I must admit that in my 2 years at this job I have never seen one fail. You might also want to check out ebay, there is always an ample supply of storage solutions (big and small) available at a fraction of the cost. If your staff are talented, they should be able to do w/o support. I strongly advise you, however, to do some homework and see what kind of community support exists for various second hand solutions.

I would use linux as a file server integrated with Samba. We deployed such an environment in our lab. haven't done a lot of testing, but share / user permissions and Win AD permissions work fine. It took a bit of work to fine tune samba config, but not long.