Sol 11 express X86:Dual monitor config,max resolution

Hello!
I have some X86 desktop computer with G45 embedded dual-head video.
Two monitors can be configured, but with "small" problem: the summ of dimensions in any direction (vert or horis) can't exceed 1680 pix- max sizeof virtual screen area.
Attempts to edit "videoram" parameter in xorg.conf failed.
Any minds?