Networking w/o a router

Does your cable modem allow BOTH outputs to be used at the same time? All the ones I've seen let you use one OR the other, not both simultaneously.

 

Hmm I've never seen that. The cable modem must have some basic routing capabilities. Although I doubt you'll be able to network the two machines locally, post the make and model of the cable modem and we'll have a look.

 

I've had a quick look at the spec sheet and userguide of that cable modem and it doesnt mention anything about networking the two pcs together through the router.

You have two options. You could either create an ad-hoc network between the two machines or get a router. Out of the two, I would probably recommend getting a router. While it would be more expensive, it would also be easier, more convenient and serve as a good firewall for your machines.