I don't know much about vocal techniques and all that stuff, but be warned !! About six years ago, I was partying with a buddy's band after they practiced and got rather drunk. I started screaming Pantera songs and stuff jamming with them and I screwed up my voice so bad, I couldn't talk "normal" for weeks and couldn't sing (I sing harmony) for about two months.
I don't think you need private voacal lessons with Pavarotti to sing metal music, but to be honest, even those goofy high school choir teachers HAVE to know some important things about taking care of your voice. I would seriously consider taking some vocal training as horrible as it might seem at first.
Here is an example:
I have been playing guitar (metal guitar) for 19 years and I have taught guitar (not at this time.) If you don't have an acoustic guitar, or won't buy one, you don't get lessons from me. Some people can't handle that, but I don't teach guitar to make money, as there isn't much money in it but I teach it to turn out musicians. The first song (rythm) I learned how to play was "Rainbow in the Dark" by Dio and I could make it sound pretty similar to the song in a couple of hours with the help of tab and the fact I played bass for about six months before I picked up a six.
Anyway... the point I am getting to is that I really didn't realize how much of a challenge making music with an acoustic guitar was until I decided to buy one. When I could really make an acoustic guitar sound good, my electric work instantly was improved ten fold. If you can learn to live with those boring exercises and stupid songs a QUALITY vocal instructor gives you, it will pay off when you go to the nasty..... I promise.
Bryant