Description of problem:

On P5B Asus board with Intel(R) Core(TM)2 CPU and 4 GB of installed
memory an attempt to boot 2.6.18-1.2798.fc6 or 2.6.18-1.2868.fc6
causes an instant lockup pretty close to a beginnig of the whole boot
sequence _provided_ "memory reallocation" feature in BIOS is _not_
disabled.  OTOH if you will do this disabling then a machine does boot
but it is loosing a gig of memory with an output of 'free -m' as
follows:
             total       used       free     shared    buffers     cached
Mem:          2948        559       2389          0         17        335
-/+ buffers/cache:        205       2742
Swap:         1983          0       1983

Updating to the latest available BIOS does not help.

A lockup happens pretty much at the beginning of the whole boot.
At least whatever is printed on a screen scrolls way too fast for
anybody to read anything out of that and after that there is no
reaction to anything whatsoever (and there is no serial port so
no way to try to capture an output that way).  I attach two
screen pictures with whatever is frozen on screen.  One from
2.6.18-1.2798.fc6 boot and one from 2.6.18-1.2868.fc6.  They do
not differ that much with an exception of "CR2" on the screen top,
which is not even in the same range, and slightly different address
for _sinittext.

Apart of these two picturea attached are a dmesg output from a boot
with a "memory reallocation" disabled, and from 'cat /proc/cpuinfo',
from 'dmidecode' and from 'lspci -tv'.

How reproducible:
As described - always, unfortunately.