Need help setting up IC for two computers...

Okay, in my situation I have the cable modem/router (It's one device) hooked up upstairs, with one ethernet cable running down into my room. From here, I have two computers that need to have internet access: My main computer, and my server. I'd prefer to have my server physically in my room and not upstairs, but if it comes to it I will put it upstairs.

I also have a crossover cable and I was wondering if there was some way for me to set up my two computers to both be able to use that one ethernet connection. My main computer has two ethernet ports, and the server has one, so I thought I could simply run the main IC to my main computer, and have the crossover cable pass it off to the server. But, in practice I have no idea how to do this!

In short: is there any way for me to share this one ethernet cable between the two using the crossover cable as well? Or will I have to buy a bridge/just set up the server upstairs?