Your site really got me interested in looking up information about this and I took a lot of what I already knew and compared it to the things I learned to get a pretty good idea about these backward messages.

Here's someone else's lyrics for the whole song...
http://web.stargate.net/zeppelin/
features/sth-reversed/index.html
Interesting how if you read the part where it says
"And all the evil, it was there, they made our souls must have Satan" and you listen to it, I still sounds like this is correct, but if you read your version it does too, I heard 'sad satan' before I read your lyrics

I listened to your part of the clip before reading the lyrics and I could hear some key things in it (666,sad satan,oh satan )but the other parts were very tough to interpret. Once someone reads the lyrics and sees them as one thing, it is hard for your mind to view as anything else until you see it a different way.

Link from http://www.popex.com/ -- if you go here it explains that it really doesn't have to be satanic, and probably isn't. The forward version says "yes there are two paths you can go by, but in the long run there's still time to change the road you're on." It basically says that this guy believes that he's saying the path to satin will make you said, he also proposes the idea that satan may be a metaphor for all sadness and suffering.

If you go to http://www.reversespeech.com/
Simple_Examples.htm it will give you many examples of things people said that say something else backwards. The guy on this site studies it.
I read partially from this site but mostly from some other site that the subconscious mind can interpret things backwards, and understands it as fact. However conscious decision making skills can override your subconscious mind. I learned before this that your instinct is based on facts you have gather. According to some, the more times you have heard those messages played backward, the more you get in your head to do these thing till it becomes a point where your instinct tells you to do something.

You should also check out Queen's "another one bites the dust" backwards if you haven't heard about it already. I won't tell you what it says backwards, because I think your view may change on what it says but it was pretty clear to me, even before I heard what the lyrics were. However I read from some biased article (with no actual proof) that 80% of people who hear "another one bites the dust" backwards didn't know what it was until given the lyrics where 100% said they thought that was correct.

Another freaky thing is the pokemon rap where it says "gotta catch em all" backwards says "oh satan, oh satan" sounds freaky, it can be found here, with many other clips of songs that appear to say something backward.
http://www.undergroundnoize.com/