Can't use higher resolution with Topcon 10" monitor

Hi,

I've just bought a Topcon VS-10S 10" monitor from shop. Shop staff had
shown me clearly the monitor could be displayed in 800x600 resolution
with 30 bit color (I didn't know his PC configuration). When I
connected the monitor to my PII PC w/ NVIDIA RIVA TNT display card, XP
Professional & XP Home installed in 2 separate HDs, I found I could
only get proper display with VGA mode (640x480). If I changed the
resolution to higher values, the display immediately turned into a
mess.

I tried forced XP to search for Topcon's driver but I found no Topcon's
brand name in monitor driver list.

Please tell me how can I use this 10" in higher resolution ? I checked
from below url that the best resolution for this monitor should be
1024x768.

http://www.aures.com/ang/2_pdv/6_monit/a_vs_10s.html