Check the X log in /var/log. It's called either Xorg.0.log or XFree86.0.log. It will contain all error messages and is probably useful - it usually is when troubleshooting X problems.
I have just ordered an NX9105 myself and from what I have gathered in order to use the 1280x800 resolution in X you need to add this to your X configuration (/etc/X11/xorg.conf or /etc/X11/XF86Conf-4), to the Modelines section:
Code:
Modeline "1280x800" 80.58 1280 1344 1480 1680 800 801 804 827
Håkan