I have a friend with an office in his house that has been using a box with win2k pro as an in-house file server for quite a while and with literally zero problems the entire time since I made that for him.
Its h/w was updated a couple of years ago and it just keeps going fine - and I will be replacing it with a Linux box sometime in the future for him.
There is just him, a secretary & a part-time assistant, a total of 3 other PCs that share files via the server (which is not accessible via internet at all).