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.
"No pressure, no diamonds" Thomas Carlyle