quite simple actually...
select the front eyebrow faces, and go to Edit Polygons >> Texture >> Planar Mapping (or something) and open the UV editor, set the size so it fits, and then, do the same for the back faces (rotate the texture 180 degrees in the Y axis (cause its the back...) and then, take a UV snapshot when your pleased with the results... go into photoshop, draw a black/white image of your eyebrows, save it, and go back into maya, and make a lambert, or whatever, and make the transparency node a file, and select the image you just made in photoshop, and thats how.....
I know I did a crappy job at explaining this, but to understand better what I mean, go here: http://www.planetquake.com/sin2q3/tutpart2a.htmhttp://www.planetquake.com/sin2q3/tutpart2a.htm
its a basic texturing tutorial, but use the same concept on the eye brow (which will be much more simple that this person) and, instead of applying a colored texture to the color node, apply a black and white image for the transparency. (I always get it backwards, but in the image you make, WHITE is the transparent part, and black will be solid)
hope this helps! 
