FreeBSD 5.1-RELEASE on IBM ThinkPad T30

[stanislav shalunov]

I'm trying to install FreeBSD 5.1-RELEASE on a new IBM ThinkPad T30 type
2366-8AU with BIOS version 2.01 (1IET58WW) dated 2002-08-06 and embedded
controller version 1.01.  I can boot from either boot.flp (burned onto
a CD) or 5.1-RELEASE-i386-disc1.iso only if I issue the following two
commands to the boot loader:

set hw.pci.allow_unsupported_io_range="1" 
set hw.cbb.start_memory="0x20000000"

If I do not issue these commands, but simply let it start booting,
the boot process freezes hard (the last message varies).

I could install FreeBSD on the hard disk (leaving Windows XP there as
well on a 6GB partition in the beginning of the disk, just in case).
When I boot the system, I see the usual prompt:

F1   ??
F2   FreeBSD

Default: F1 

If, at this point, I press F1, Windows XP will successfully boot (and the
default will be F1 next time).  Pressing F2 causes the machine to pause:
the cursor continues to blink, control-alt-delete works, even F1 works,
but the machine just sits there with a blinking cursor and does not
even start to boot FreeBSD.  Should I reboot the machine while it is
waiting like that, the default next boot cycles will be F2 (but again,
no attempt to actually boot FreeBSD is seemingly made).

I've used the fixit CD to mount the root partition and change
/boot/loader.conf to read:

hw.pci.allow_unsupported_io_range="1"
hw.cbb.start_memory="0x20000000"

That didn't change anything.  Not that I had a lot of hope: I don't see
any evidence the machine gets to read any of the boot config files...

Am I doing anything wrong?  Any hints?