The 10 user limit will haunt you as you will find out.
I'll ask why not Linux? You do realise that with XP you have to feed and care for it almost weekly it seems as the pests, worms and what else seem to show up constantly. Just last week you see that patch it again...
By moving to some other solution you get to miss out on that fun without the expense of the OS.
Linux's ability to serve files and printers is there. User accounts and more is there and you can use a Web browser to maintain it. Diskquota on the server is there. In fact the only piece missing might be you.
Bob
As best I can, I provide hardware (and some OS support) to a local K-8 parocial school where my wife is technology coordinator. As usual, the administration has no clue as to how to budget for computer technology. Currently, the facility has a computer lab with 12 PCs and one in each classroom for student/teacher use. There are also other PCs in the library, etc. All are networked peer to peer. Most are still running Win 98 but my wife has purchased licenses to install XP Pro on all computers, most of which are not hardware capable of running the OS at this point. The project I have been asked to undertake is to set up something of a file server so local machines do not fill with redundant data and users don't keep losing there stuff on the network. The move to XP Pro should also provide considerable security advantages. The file server would basically be a storage device and be used by teachers and higher grade students to store and retrieve their own work and group projects. We would have to create folder space and manage permissions for all users. I would move the "My Documents" folder for each logged in user to the server. My home network has several PCs and I run XP Pro, Home or Win 98 on these. I have been successful in creating the basic concept on my home network with the exception of being able to set disk space quotas. My question has to do with XP Pro's limitation on simultaneous usage. I believe there is a limit of ten users at one time but I doubt this would occur often especially if we can teach people to always log off when finished. Does anybody know if this would work and what pitfalls there migh be. Thanks in advance.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic