Go to the gradients palette and make a new gradient that begins with 100% opacity and ends with 0% opacity (I used white, but itΓÇÖs up to you.). Use this gradient to fill the space inbetween the lines of the shape you have created, using the lines with the gradient fill. If the gradient is going in the wrong direction, you need to use the fill modifier tool to either rotate, scale, or move it. The gradients should be at their whitest inside the letter, moving to 0% transparency at the outside.
