See both way of accessing is different. If you plan to setup a server enviornment then your SBS will act as a domain controller and you will have better control over your users and resources on the server.
But if your main purpose is to share files without any security concern then making a shared folder on a windows XP box is the best bet in a workgroup environment.

Let me know..

sbs will do. so will xppro for 5 clients.
actually the simplest and cheapest is a linux box with samba (it also has no user amount resrictions) or something like freeNAS

post hijacking?