1.boot from CD, proceed as expected until you get to the first reboot stage
2.hold down C during reboot to force it to boot Mac OS 8.5 from CD once more
3.run the System Disk tool, use it to set the Mac OS X server partition on
the CD as the system disk and on the advanced options screen select "Stop
at Open Firmware."
4.do a SHUTDOWN not a RESTART.
5.power up and it should boot to OpenFirmware.
6.type boot and it should boot the Mac OS X Server partition off the CD.
7.after the install completes successfully you can use the System disk tool
to reset the boot procedure anyway you like.