Is it possible that you put the starfield in as a background instead of a backdrop?  The background is displayed on a large virtual sphere and often causes such a blurring effect on an image close to the size of your finished image.  If that is what you are using (like a 1024 x 768 image for the starfield behind a final render of 1024 x 768), then you should use a backdrop, which is a 2D plane which remains perpendicular to the camera, behind your screen.  The jpg will then be clean and clear.

If you are using a smaller jpg than your final render, try tiling it as a backdrop.

One thing - the backdrop will remain static when you move your camera.  With a starfield this should not be a big issue unless you are animating.

If you are animating, you could try tiling the jpg on the background sphere.

Klebnor

Lotus 123 ~ S-Render ~ OS/2 WARP ~ IBM 8088 / 4.77 Mhz ~ Hercules Ultima graphics, Hitachi 10 MB HDD, 64K RAM, 12 in diagonal CRT Monitor (16 colors / 60 Hz refresh rate), 240 Watt PS, Dual 1.44 MB Floppies, 2 button mouse input device.  Beige horizontal case.  I don't display my unit.