In 00xserver-xgl_start-server at the line 24
replace XGL_BLACKLIST="nv vga vesa vmware" by XGL_BLACKLIST="nv vga vesa vmware fglrx avivo"
Doing that you will start on a standard Xorg (no XGL) so no desktop effect but you can run openGL application like google eartgh
In 00xserver- xgl_start- server at the line 24
replace
XGL_BLACKLIST="nv vga vesa vmware"
by
XGL_BLACKLIST="nv vga vesa vmware fglrx avivo"
Doing that you will start on a standard Xorg (no XGL) so no desktop effect but you can run openGL application like google eartgh