I know what you are talking about. I am developing a game, and the problem I have is that after crashing a few times, the game reverts to software open GL the next time I run it. This is on win98 with TNT2 Ultra.
I also tested it on a machine with a Riva 128ZX and it will only run in hardware mode if the res is 800x600 or less and 16 bit color (that may be a memory size limitation, not really sure).
Today, I just tested the program on my friend’s Prophet 3D DDR Geforce 256, and I could not get it to run in hardware mode at all (even if its the first thing I run after booting up). Other openGL software works perfectly in hardware mode on his system.