Well, .PNG images are not as big as .BMP images. A good image editing program like Image Analyzer, Paint.NET or GIMP can convert the .PNG into .JPG. But .GIF is even smaller.
(PS: Some people said they couldn't download the cars file from MediaFire. Actually, it is RAPIDSHARE who corrupts files. I have experienced trouble with a file on RS and other 729172938 files uploaded there.)