It might also be wise to limit access through the router to the specific MAC addresses of the computers you are using. Each network card (whether wired or wireless) has its own unique ID, so in theory (and pretty much in practice, I would guess), that would prevent unauthorized access--but the encryption would still be necessary to prevent evesdropping on the wireless connection.

The process for setting this up will be specific to the router, so you should have a look at the manual or documentation.

I should note that I'm not an expert in this area, so someone correct me if I'm wrong on any of these points.