Looks like a good start man. Just keep adding bits here and there to define the shape a bit better. Its a lot of fiddeling about moving verts etc but you'll get there.

I also like to use the sculpt poly tools to define areas just by gently puching an pulling with the auto smooth on.

Are you using maya 2008? If so I would recommend using the smooth poly preview at this stage to define areas on the lor res with the preview on to see hos its going to look smoothed.