First off, having the words GameShark mentioned so many times and about gameshark, this should have been in the hybrids and gameshark section (Neon Duke or Der Alta, please assist) Any ways all the game shark/action replay is, is a hacking device that alters the value of a hex code. Game Shark and Action Replay are one in the same, just that Mad Katz owns the legal rights to Game Shark, and Datel to Action Replay. Another big cheating device is Code Break by Pelican (Nathan you trater!). Code break is supposivly easier and more advanced, i saw no difference.
Now the Shark Cable you were talking about is a nifty little divice call the Shark Port (Mad Katz)/ X-port (Datel). Sadly the Shark Port is no longer in production but Datel is a cool company because they have re-did the origanal X-port coming out with V2.2.3 i think or something like that. To answer your question, you use the USB ports on your computer and ps2 to transfer stuff, but you have to use the X-port/ Shark Port cables because it has a small transfer case that basicly translates the info for the computer to be able to read it, saly it doesnt allow you to play on the computer. But you can put codes in alot quicker with it.
Alot of the Shark Port/ X-port owners use theres for Hybriding cars (Thank you Nathan, Famine, Heydu, and Anthony) You can do that with just a game shark, but it kinda gets sloppy using trying to make sure you put in the correct codes. A good buddy of Nathans did this neat thing called the MK Program (thank you Mr.MK) wich alows you to use the value of one car (put really huge tires like the Supra Tires) Put them on a Gt-40, put on parts that have the most horse power, do a power multi, and then have it about 10 mm off the the ground, you get it to do the 400m in 3.750, no kidin, my friend did a merc that did it in 2,000 (Darn you Anthony!)
Ok this is what you need, Get a GameShark Version 2 to 2.2 or an Action Replay (not max) these are currently the best ones. Mad Katz quit doing codes for the gameshark, but Datels loves us so much they continue. Search E-bay for Shark Port or go to your local Best Buy and get an X-port. You will never regret having them.