How to hook up ps3 internet useing ethernet cable?

how do you hook up the PS3 to the internet useing the ethernet cable? Apparently it has to go in a LAN port, well my modem only has one LAN port and its being used by my computer of course... Does your computer have to be online at the same time to get a connection from the ps3? can anyone give me instructions for hooking it up?
I have comcast cable internet by the way if that makes a difference

You'll need to get a router, or disconnect the computer from the lan port to use it for the Ps3.

A cheap router that works well will run you 30-50 dollars at Best Buy or similar. You might first try using the cable & removing it from the computer though to see if that works.