Most all of the large presentation monitors like your unit top out at 1024x768@60Hz
What refresh rate at the XGA resolution are you sending to the monitor?
Have you tried a different PC to see if the graphics card you experienced issues with is partially to blame?
Also, most of the large CRT monitors don't look very clear when using over 800x600.
On top of that, if your monitor has seen alot of use, the picture does get fuzzier - especially at 1024x768!
The s-video connection you described is not sending a full XGA signal (resolution is down sampled when outputting via s-video).