I just bought a Playstation 3. I want to connect it to my computer so I can play online. When I tried to do ?

May be...

this using the ethernet wire that came with PS3 I noticed that my modem only has one ethernet imput (for connecting to my computer). How can I connect, both my Playstation 3 and my computer to my modem (I have Cablevision's Optimum Triple Play) at the same time?

you need a router