Well since the Monitor is younger than your OS then you are going to get issues like this, e.g. it not having a specific driver for it, so you will be getting some sort of compromise generic driver.
You could try downloading the driver and installing it, drivers tend to support OS versions, but some that come out may be backwards compatible or the driver is a huge size incorporating multiple OSes. So I'm a little surprised to find that this one is 118KB, I would have thought it would have been in the order of 10-20MB not KB.
Though it says it is compatible with win98, see image, however these mention HP systems and not specifically monitors, so I'm not entirely sure what it is.
I would stick with the mid range of colour as 24bit true colour would probably be to much for your graphics card/chip and 256 colour is absolutely disgusting.