I'm using Win 98 with S3 Trio card, Philips Monitor 104s 14"

I'm trying to set screen resolution to 800x600 but its making characters very small & not fully utilizing the monitor (space at the right end side is not being used)..

currently the monitor type is set to unknown monitor and I tried to search driver for this particular model but was not able to find it...

can anybody advs. me how to solve this ??