Get a program called TS 404 from http://www.threechords.com/hammerhead/ts-404.shtml and SimSynth http://www.threechords.com/hammerhead/simsynth.shtml and other sound generators from http://www.threechords.com/hammerhead/apps.shtml
Now get Audacity http://audacity.sourceforge.net/ for recording and editing.
Check out this tutorial that covers everything you need to know about Audacity: http://www.mp3soundstream.com/Audacity_Tutorial_-_Free_Audio_Editing_Software.html
Get the LAME MP3 Encoder from http://lame.sourceforge.net/
Check out this tutorial that explains how to setup your sound card to record from the sound generators and other programs: http://blogs.msdn.com/alexbarn/archive/2005/03/01/383359.aspx
(Only do step 3)
Check out this short tutorial on Setting up Audacity and recording with it: http://audacity.sourceforge.net/manual-1.2/tutorial_basics_4.html
