This is probably what you're looking for anyhow...but start by practicing to some Metalcore songs, I personally hate the stuff but the style is much easier to pick up and build further upon. Killswitch Engage has easy to imitate vocals and don't require a whole lot of skill to perform so you probably won't tear up your voice too bad. Once you get those type of vocals down ok and you want to pursue Death Metal vocals start by doing some Morbid Angel type stuff, maybe Hate Eternal as well. It becomes a little more difficult when you actually start developing a unique style whether it be the easy to understand, mid-end screams of Johan Lindstrand or some of the higher stuff done by Peter Tatgren from Hypocrisy.
Black Metal vocals were a little harder for me to learn. Practice to the Wrath of the Tyrant demo by Emperor as Ihsahn at the time was very raw and undeveloped with his vocals. Just remember this, your screams can sound like shit and you can still be a "good" Black Metal vocalist (Burzum). I'd say to go for a style like Ihsahn, more convetional type stuff like Abbath from Immortal or maybe Maniac from Mayhem for those real fucked up sounding vocals.
If you're just looking to do Hardcore/Metalcore screaming and you just happened to confuse the genre as "Metal" and not "The illegitimate, unwanted bastard child of Metal" then just get some Killswitch Engage type stuff and practice to that...you should be screaming aquedate in a week or so.
