First, is this shield curved or flat?
Draw spline, not too many points, arround shield, extrude, convert to editable poly, cut inner shapes, chamfer, bevel or extrude, play a little bit.
Also, this is awesome tutorial for modelling, check it out! Helped me a lot.
http://vimeo.com/10941211
EDIT: Do not mess with splines as you show in second picture. Just draw a basic shape around picture and try to block model basic object. I will try to show you how, give me a day or two, cause im not at home.