If it's feasible for you, I'd definitely recommend going with intel or amd for your next gpu, due to the whole FOSS drivers/specs thing for one, and yes-- I have had problems with my geforce 8400m gs. I applied a bios update, and it's been stable since, but I haven't stress tested it yet-- I should do that soon. Good old nexuiz
Also, If I recall correctly, the X4500 is /already/ brilliantly supported under Ubuntu Intrepid and such.
I hope centrino 2 isn't expensive just because it's new, I'd certainly go with it-- intel is amazing with all their drivers, none of this broadcom wireless or creative sound garbage.