>Can someone tell me how to tell the difference between 
>a male and female Guinea Fowl?

Not being an expert by any means, I have found that *my* guinea hen turned
out to be the one who had somewhat "curled" wattles.  The male's wattles
(the red, fleshy part that hangs under the head on both sides) hang straight
down.  The hen's wattles curled under the head a little. 
-=-
The sure difference is that the female
is capable of making a certain noise that the male can not make.  They can both
make that ear-splitting loud cry, but the female makes another sound when she's
a little less agitated.  I'll try to describe the sound as best as I can:  it's
a two-beat sound that sort of sounds like a question.  It's like, "wop-wop?
wop-wop?" with an accent on the second wop.  Hope that helps!