Technically, it's hard to find a hub anymore. Nearly all the 'hubs' are switches now. As a guideline, if you send a packet and lights for two ports flash, it's a switch. If you send a packet and lights for all ports flash, it's a hub. A hub blindly rebroadcasts every packet to every port. A switch is selective.
You'll need a switch/hub if you want to play with a third computer, or if you get a DSL/broadband/etc. network device that you want to have available to both computers, whichever is one on/off.
Keep in mind the crossover cable is 'special'. It should be a different color than your other cables, or otherwise marked. There's usually one extra plug-in point that shares a port on a switch/hub for plugging into another switch/hub, and you can plug the crossover cable from your computer into that, if you like. (Because this 'extra' port has the crossover wiring, that effectively makes a crossover cable into a 'normal' cable.) You can't plug another connection into the other half of that port. Well you can... but it won't work. The crossover cable will not work on any of the other hub/switch ports: just to save you discovering that for yourself.
The other nice benefit of switches (and external MODEMs): A little christmas tree light show!