I might have..

According to http://www.xfree86.org/~dawes/845driver.html - [Why can't
I get high resolution/depth modes?]

*snipp*

The Intel integrated video hardware uses a "unified memory
architecture", which means that video memory is allocated from normal
system memory. Most BIOSes have an option in one of the configuration
screens to set the amount of system memory that is set aside for use as
video memory at boot time. If you are having problems using high
resolution or high colour depth modes, this is the first thing to
check. If your BIOS configuration has such option, change the video
memory amount to 8MB or higher, and the problem should be solved.

Unfortunately not all machines have such a BIOS configuration option.
It if often the case with laptops that the amount of memory that gets
allocated at boot time is fixed at 1MB (actually 832KB). Although the
XFree86 driver can and will allocate more (if the correct agpgart
kernel support is present), the mechanism used to inform the video BIOS
of the additional allocation doesn't seem to be implemented on these
laptops. This results in the video BIOS refusing to program video modes
that require more than 832KB.

*snipp*


It seems that this could be the problem..
What do you think?

Brgds Robert