The bounce buffer is normally allocated at the top of ram - 2* the size of the LinuxBIOS ram segment. It would appear that its got the wrong idea about the size of ram in this case.
One thing I have determined from going through the 430tx raminit.inc is that raminit sets up 64M of memory, then 128M. It is _not_ autodetected, and does _not_ use SPD. This is contrary to what I had read, but it was admittedly for another mainboard.
In other news, I managed to get BOOT_IDE to work, and managed to actually boot a kernel!
Regards, Andrew