Get Reaper (free recording-software), and a Line6 pod.
http://line6.com/podx3/You don't basically need anything else. Except guitar ofc ._.
In case you dont want to purchase anything, put a cable from you amp's "line output" to computers "line input."
Then set the incoming "microphone recording" as "line input" from Windows' options. You should be able to record now.
Though the sound will be very raw, and you are probably going to suffer heavy lag due to Windows' & line input's communication.