LAN setup

I am using dsl internet and have a 4 port router installed with 3 comps running.
Two comps are in same room as router and third is upstairs hooked with a 65 ft cable to router
I work on other comps in the room upstairs and have to move the cable from comp to comp to access internet
My questions are this :
Can I use a crossover cable to hook fourth comp to the third comp to access internet to eliminate have to constantly move cable back and forth?
I assume this would require that comp #3 have an ethernet card with two ports or is there another way to connect together without having to replace the ethernet card?

Many Thanks for input


Major Geeks Rules

 

Get an Ethernet Switch, attach the cable going upstairs to that, then you'll have an extra couple of ports to attach other devices.
Something along these lines:
http://www.komplett.co.uk/k/ki.asp?sku=321792

Simply plug the cable to the router into port 1, then plug each device into the remaining ports. You might need some extra cable for this, CAT5e (or 6 if you want... ) straight through (NOT crossoever)