Set it to non-interlaced mode. Interlacing is method where the electron guns in your monitor alternate between drawing odd and even lines. The only real advantage that an interlaced display has over a non-interlaced one is that it can drive lower refresh rates without flickering. But the big downfall to an interlaced display is the "flutter" produced in video animations (i.e. if you play games or work on video with your PC, this is very important). The NTSC telivision standard runs at interlaced resolution, but 99.9% of today's PC displays run at non-interlaced resolutions.
Furthermore, I tend to doubt that your monitor can actually display very many interlaced resolutions.