Yeah I've got a DNS-323 (
http://www.dlink.com/products/?pid=509) so it's just an enclosure, then buy a couple of hard drives (I wanted to be able to mirror them to protect the data from hard drive failure).
Right now it's 320GB, but I'm not doing much video so that's tons of storage (all shared files, all PC backups are autoscheduled and go up to the NAS).
Costs would be higher for a Windows server of course, but as you say it might be easier to use and it would have more features.