BTX halted when booting from CD: Toshiba M10-10i laptop

Hi all,

I've got a new laptop (a Toshiba M10-10i, for the archives) but FreeBSD
won't boot on it.  I've tested with the May 2009 amd64 snapshot ISO, and
about 20% of the time, it hangs before even displaying "CD loader".  The
rest of the time, I get the following BTX register dump:

CD Loader 1.2

Building the boot loader arguments
Looking up /BOOT/LOADER... Found
Relocating the loader and the BTX
Starting the BTX loader

BTX loader 1.00  BTX version is 1.02

int=0000000d  err=00003d58  efl=00010246  eip=3583d321
eax=8b16d000  ebx=00000000  ecx=ffff0000  edx=00002170
esi=00000000  edi=0003b7c0  ebp=00090bf8  esp=00090bc8
cs=002b  ds=0033  es=0033    fs=0033  gs=0033  ss=0033
cs:eip=07 00 00 00 00 00 00 00-33 00 02 00 00 00 00 00
       00 00 00 00 00 00 00 00-03 00 00 00 20 00 00 00
ss:esp=5b 3d 03 00 33 00 00 00-48 01 00 00 a0 b0 03 00
       38 00 00 00 6f 01 20 00-1a 00 20 00 01 94 00 00
BTX halted

(at which point the laptop immediately reboots.  This is transcribed
from a photo.)

A second crash (some registers are different, but I guess it's the same
cause due to the same odd eip):

int=0000000d  err=00003d58  efl=00010202  eip=3583d321
eax=79f7b814  ebx=00000000  ecx=02000000  edx=000000ec
esi=00000000  edi=0003b7c0  ebp=00090bf8  esp=00090bcc
cs=002b  ds=0033  es=0033    fs=0033  gs=0033  ss=0033
cs:eip=07 00 00 00 00 00 00 00-33 00 02 00 00 00 00 00
       00 00 00 00 00 00 00 00-03 00 00 00 20 00 00 00
ss:esp=5b 3d 03 00 48 01 00 00-a0 b0 03 00 38 00 00 00
       6f 01 20 00 1a 00 20 00-01 94 00 00 00 00 00 00
BTX halted

Now, I can tell that eip is off into the weeds, but I'm not really sure
how to debug this past that.  The first address on the stack is
presumably a return address, but that doesn't seem to be within the
address space where any of the bootstrap code is loaded to, so maybe I'm
wrong. 

So, how do I continue tracking down the problem from here?

I don't know if it helps at all, but even a 4.x CD dies in BTX (although
I haven't managed to successfully take a picture of that to confirm if
it is the same problem, but can try if it would be useful)

As an aside, from what I understand from the source, once we've got to
this stage of the boot the environment should be the same whether we're
booting from hard drive, CD or PXE?  Is that correct?

Thanks,

Gavin