ok first u need to install ur cod 4 to xex menu its very simple make a new folder called cod 4 and go in it and hit copy dvd then ur tray should open put the disc in and close the tray by pushing it in DO NOT USE THE BUTTON wait 5 to 10 seconds then hit copy after u have it install go to the downloads section and type cod 4 patch download that and put it on a usb then put that into ur jtag go to ur usb copy the patch then go to cod 4 and click A then paste the patch and then hit default xex then hit multiplayer systemlink host and start it make sure ur retail and jtag are hooked up to the same router with ethernet cables hope this helped plz rep