I ran Win98SE on mine for a few months. Although I had some stability issues, I believe it was becuase I was using two sticks of memory. Once I pulled one of the sticks, the problems seemed to go away. I was getting BSOD. Other than that issue, I had no problems with the Win98SE drivers.
I have installed 2K Pro on it, but not NT 4.0. Again, I didn't have any driver problems with 2K, but I didn't really use it. Just did a test install, installed office 97, and played with it for a day or two.
I currently run Debian Woody on it. I haven't tried sound or usb as I have no need for them. There is a problerm with the exisitng Trident driver for X. You cannot switch from X to a console and back again. You need to kill X and restart it. Apparently, there is an unofficial VIA trident driver, it may fix this problem or not. Some guy on this forum
has a link to the driver in his sig. He got it for VIA by emailing them. I run X at 1024x768x32 on a monitor.
I run two Zalman Fan Mates on by board. They fit nicely between the top of the ports and the top of the Cubid 2677 (not R) case. Using them, the louest thing in the case is the hard drive. They make the machine virtually silent.
As far as DOS games go, I did a test install of Quake (the original) for you. I would say that it runs decently at 640x480. However, it started to get choppy at 800x600. I would have tried Duke, but a friend in another state has my copy. I suspect it shouldn't be a probelm as it isn't truly a 3D game (if I remeber correctly
There is one thing to note about running DOS games on the EPIA boards. For some reason, VIA didn't ship all the drivers you need to get sound working in DOS. They are missing a driver called VIAFMTSR.COM. I found a copy by searching Google.
I also ran MAME when I had Win98SE installed. It played just fine for my tastes. Granted, I was running old school games for the most part. The most stressful thing I played was NEO*GEO Ninja Combat. The performace was about what I remember from the arcade.
I also was able to play Duke Nukem Manhattan project on it using the lowest settings.