Spea,
You'll probably want to try it two ways and decide which way you like better. For different voices/equipment and environment, you'll get different sounds. Try a few screams, layer them with about 10ms delay, maybe a little plate reverb, compress the hell out of them and see how it comes. If that doesn't work, try getting 3 or 4 of your friends around a condenser and go at it. You'll probably need to compress and add effects, but try these methods and decide which works for you. Never be afraid to try something out. If it suonds like shit, do it again =)
...Not the most fun, but the most rewarding way...