I finally managed to make the Rage128 accelerated Xpmac X server work under Debian PowerPC on my PowerMac 7300 with a Rage Orion card. It turns out that I'd forgotten to download the 75dpi fonts. The font path is hardcoded in Xpmac and the Misc, Speedo, Type1, 75dpi and 100dpi ALL need to be installed for the server to start. I thought I didn't need the 75dpi because I have a 19" display but...
So this is a solution for people who need an Xserver working right off the install on their machine, without having to play with X86Config first. My Debian system is almost working perfectly. The only package that is still broken is console-data (and, because of that, console-tools), that doesn't have any PowerPC info. I've noticed that, after installing, my console has become EXTREMELY slow to refresh (it was fine while I was doing the install). I assume it's related to console-data/console-tools not working. Very happy, Renaud