The network adapter is this device that you plug into the back of PS2 that allows you to play online, it cost 39.99 US dollars but im sure if you shop around you may find one cheaper. The network adapter is where you plug in the cable from the router, its pretty simple once you get it, it maybe takes 5-10 min to set it all up.
If you get SOCOM make sure to get SOCOM 2 because there are tons of cheaters who use gameshark and codebreakers to get an advantage in SOCOM 1. They elimated this in SOCOM 2 (thats what Sony says).
I couldnt agree more, i hate when certain games only come out for one system.
Here are some screen shots.