Future plans will include building the Xpmac server from scratch. However, that has not yet been implemented. You don't need an ATI Rage 128 card nor do you need USB to use this server.
Unpack the Xpmac archive and install it by running:
cp Xpmac.rage128.usb.rev9 /usr/X11R6/bin
cd /usr/X11R6/bin
chmod 755 Xpmac.rage128.usb.rev9
ln -s Xpmac.rage128.usb.rev9 X