How did you boot the install? The "Read-only file system" is the issue above - no modules are loading.
Did you specify kernel-options "root=/dev/ram3" and "ramdisk_size=36000"
(after selecting the right kernel & initrd)?
Thanks for the hint... adding "root=/dev/ram3" did it. (RTFM?) But I wonder, why did it work with the old kernel without that? What does BootX use as root by default? Ramdisk size was set to 40000 using BootX' ramdisk size field. Graphical installer works well now. I can't do an install at the moment though because I don't have any HD space left on the Wallstreet. Maybe I'll dig the second SCSI HD out of the 7300 to test it.
By the way, what I miss from the new installer is being able to click "Exit Install" in the steps list to reboot. There's a quit button in the license agreement dialog, but none in the later dialogs, so I haven't found any other way than force rebooting ("shutdown", "halt", "reboot" from console 2 don't work either).
-Christian
