Originally Posted by stevebrot 
To add to Sean's comments...There may also be some metering issues with the screw mount lenses. This does not make sense on initial thought, but lenses lacking the electrical contacts on the mount apparently do not provide adequate information to the camera for the meter to give an accurate reading. Go figure.
This issue is pretty pronounced on the K10D and K20D and usually takes the form of severe underexposure at wide apertures. I don't have first-hand knowledge with the K200D except that the owner's manual makes note that exposure may not be accurate with m-42, Pentax-M, or Pentax-K lenses.
Steve
And to add to Steve's comment - the good news is that you can "play" with your exposure settings after looking at the image on the rear LCD - you don't have to wait for the film to come back to check your exposure. Since you'll be in manual mode (most likely) it's easy to change the exposure settings. Also, become familiar with using the histogram to check exposure. Enjoy!!