Pentax K100D S has a
6.0MP APS-C (23.5 x 15.7 mm ) sized CCD sensor . On the other hand, Pentax K200D has a
10.0MP APS-C (23.5 x 15.7 mm ) sized CCD sensor .
Below you can see the K100D Super and K200D sensor size comparison.
Pentax K100D S and Pentax K200D have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Pentax K100D S has 66% larger pixel area compared to Pentax K200D, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.