Dude if you're into any religion, try asking your "seniors", or those who used to listen or still listen to all this stuff.
Not trying to be sarcastic or anything, google.com. Seriously, some of those guys know a lot more than us. There's Black Metal, un-Black metal, Christian metal, Slayer with the whole inverted pentagram who has a Catholic/Christian(I'm not sure) member. Otherwise you can try guitar4christ.com... I'm pretty sure some of the guys there know a thing or two about metal and satanism and the knitty gritty details.
In my opinion, there are so many angles you can look at metal at. The rage in the music(even Christian metal) itself can be considered anti-Christ and is therefore Satanic. Then there's the lyrics, the context, the this and the that. It really depends on how you look at it and what you get from the music, how it affects you as a person.
I hope my post isn't too religious.
My 2 cents worth.