File size and image quality changes

Vector Images (.DXF) are made using mathematics, angles, percentages etc. instead of pixels. This means the file size of a vector image is much less than the file size of a jpeg image. This also means because the mathematics dont change with larger images the image keeps its quality when resized.

Vector Image:

Although this image is saved a a Gif you can still see how mathematics are used to create the image, meaning it can be resized without the loss of quality.

Jpeg images:

As you can see when left at the correct size Jpeg images are much more detailed than vector images, but when resized most of the quality is lost.

Compression techniques such as WinZip will compress the file to make it as small as possible. When unzipped the image will be the same file size as it was originally and still have its original charactoristics.
Image resolution is the overall detail level in the image, because .DXF is a vector image the overall image detail is not as high as it would be if it was a jpeg. The colour depth of an image is the bits per pixel, the more bits in a pixel the more colours are available to make the image more lefe-like. Vector images dont use pixels so this doesnt come into effect untill the image is pinted, and then its down to the printer defaults.