a hub is cheaper and will work, but you'll be happier with a switch. here's the math:
since a hub broadcasts to all ports, if user1 (on port1, etc) pulls some 500MB file off of user2 (on port2) every other port is going to be flooded by these packets not intended for them... so user3 and user4's game of BF1942 is going to utterly die and disconnect
with a switch, user1 can pull from user2 and user3 and user4 will have no idea what is going on. if you can garuntee no one will be copying files, a hub will be fine, but let's face it, any one who has been to a lan party knows that's just not the case, "hey stop steal my pr0n!"