I recommend Server 2003, however you can try to do it with XP if its just a file sharing. Win XP supports raid so there shouldn't be any problems. Kepp in mind that if you get Server OS you will need licenses (multiple = number of workstations) if you use XP only one license.
Test it with XP join it to a network and see how well it works if it doesn't work well you can always buy Server Os later.
good luck
Test it with XP join it to a network and see how well it works if it doesn't work well you can always buy Server Os later.
good luck