Credit Spreads: Probability and Volatility

Lightspeed said: "Hi Guys, I thought I had some small measure of understanding credit spreads until I started looking at what some of you have posted, I realize then that I have quite a ways to go...lol. I have seen the charts posted by Holzie and had the faintest idea of what anything meant. Yet from reading all everyone has said, it seems like probability and volatility have a big influence prior to getting involved with a credit spread. SO(!), where do I start to learn these factors and how they relate to credit spreads? How can I read one of those charts, and, is there a software, that I don't have to shell out an arm and a leg for, to apply all this to? Thanks for all your input. Cheers! Gavin"