In April 2022 I heard from Robin who had been trying to install Windows 98 on his RWT205CE.
His first step was to track down the necessary drivers for the SiS 550 - which took a while. "These were found on an ICOP FTP server for another device which uses the SiS 550 (an eBox mini pc).".
For those wishing to try this out here is the zip file with the drivers.
Robin also added:
I was intending to install a sound card for FM synthesis and midi output, however in practice I have found these to behave quite erratically in this machine. I can install the drivers, Windows reports no resource conflicts and sometimes I can get it to play wave files and midi files accurately but there are often crashes and sometimes the card is not recognized at boot. More telling perhaps is the constant noise coming from the output - for example it sounds as though I can hear the serial data from the mouse every time it is moved.
I noticed that the design of this machine is very similar to that of the Fujitsu Siemens S200, and your page there mentions an issue with the lack of 12v, which is also the case here. I successfully installed a step-up converter to rectify this issue by using your suggestion of tapping into the unpopulated filter capacitor holes. There is plenty of space next to the CF card slot to fit this. Unfortunately, it didn't improve anything.
This is currently a work in progress.
Any comments? email me. Added April 2022