Well, to compress your image, i would save it as a jpeg. They are about 10x smaller in file size. What was a 20mb bmp, can be a 300k jpeg.
As for the model, I would remake the windshield to be more clean. Those faces in the middle are very ugly, just make a new cube, scale it and stuff, then subdivide it so that you have a line of verts going down the middle. Then you can raise those for a nice rounded effect.
EDIT: Lol, 3 posts at the same time.
Also, if you are concered about the image quality of the jpeg, Paint has a crappy exporter so just open it in GIMP and save it as a jpeg with quality at 100.
Im sick of Master Chief soo...ooga booga!!
Explain to me why some people pay money for 3d software? Its not 3d till its been blended. wwww.blender3d.org