Episode 1: Multi-track recording for free!Really basic information how to connect microphone (1/8" TRS jack - or 1/4" TRS jack using a converter), how to check out Windows settings for it and how to make Audacity software up and running.
Audacity is free open-source project:
Accompanying blog post: http://virgo47.wordpress.com/2009/05/18/multi-track-home-recording-for-free/
As someone mentioned in comments (thanks), this is really not the right way - it's the cheapest way. You should use preamplifier for the microphone - be it some little box, or on an audio interface or on a mixer. For more information about this check episodes #5 or 6: