Upgrading ZV5000 notebook video/mainboard?

I had my laptop apart to the bolts last night (pray that if a part on
your ZV goes, it is not the soundcard, as that appears to be the most
buried piece of hardware...). Anyway, I had the machine apart and I am
now stuck on the idea of upgrading the video.

The laptop is currently running a GeForce4Go! (or something like that;
64mb I believe, I am not at home). I know that newer ZV models have
128m Radeon x200 or better. I am reasonably certain that I cannot
seperate the mobo from the video adapter (though I would love to be
corrected on that if mistaken), but i would be willing to swap out the
entire mainboard to get what I want.

Does anyone know, or know a way to find out, if other ZV-series mobos
can swap in cleanly? For example, I have seen zv6000 series boards in
the $300 range, but the form factor looks a bit different -- the cut of
the PCB is obviously different, but I am not certain that will keep me
from swapping it in. I guess I am looking for an HP repair guy who has
seen all the guts, or some website that covers laptop opgrading
compatibilities/techniques... or something. Even if someone knows a
good source for junk parts, I'd be willing to open the thing up again
and try to mount a fried mobo just to see if it goes in.

Thanks in advance for any info!
-m