A switch is always worth it, especially nowadays since they are sooo cheap!
if you are not doing alot of file swapping and other forms of data moveing on your LAN then a hub would be fine to just connect you for rare file transfers and sharing to the net.
For more bandwith go with a switch.
The math is as follows:
If you have an 8 port 10/100bt switch the max rate is 100mbit/number of ports in use.
So if your hub has 8 pc's connected and they are all on moving data, your 100mbit is dvided up between all available ports.
With a switch each port has 100mbit dedicated to it, no sharing.
As you can see this makes things alot better!
