There are no adapters capable of converting DVI's Dual Link speeds to HDMI. All DVI to HDMI (active or passive), are single link only.
On top of that, not all monitors are recognised as high refresh capable ones under Win98 (.inf monitor driver may be required). If your monitor doesn't have it, software with custom resolution setup (like either NV/ATI's driver control panel or 3-rd party software with build-in capabilities like PowerStrip), is required to add supported modes manually.
I highly recommend buying a good/higher quality VGA to DVI/HDMI adapter, for better chance of reaching higher refresh rates on DVI/HDMI monitors (VGA makes it compatible with A LOT more retro GPUs, which is more important than pure 85Hz+ refresh I think).
DisplayPort on monitor side is a bit different ball game, but from my limited testing - adapters for it have the same limitations as DVI to HDMI ones.
Sadly, I don't know how monitor with Dual Link DVI requirement will behave when connected through VGA to DVI adapter.
EDIT : WARNING
I mean "ADC" convertion only when I mention VGA to DVI/HDMI adapters (GPU = VGA, monitor = DVI/HDMI), and NOT "DAC" ones like in DVI/HDMI to VGA case (GPU = DVI/HDMI, monitor = VGA).
This is VERY important, as there are many DVI to VGA adapters (DAC), which DO NOT work in reversed order connection (ADC).