Hi Adrian,
are you using the 1.5-rc source tarball, or the git repository? We have started to implement the X11 support directly as Backend in parallel to DirectFB. If you want to compile with "disko x11" you have to add "enable-x11=y" to the make commandline.
If you want the old DirectfB X11 backend just omit this option. If You plan to utilize X11 you should stick to the git repository until 1.5 final is out.
The new X11 backend was necessary, because directfb lacks the possibility to display video streams to the XV interface of the X-server. The current X11 backend of DirectFB is merely used for development purposes. The usage in a productive environment is currently not intended. Allthough that will change with DirectFB 2.0, we decided that we can't wait that long

Our X11 backend depends on the availability of a XV - port on the X-server.
To configure the backend you have to set some parameters in the <dfbsettings> section of the diskorc.xml:
<dfbsettings >
<parameter name="xres" value="1080" />
<parameter name="yres" value="606" />
<parameter name="outputtype" value="x11" />
<parameter name="videolayerid" value="0" />
<parameter name="videolayerpixelformat" value="YV12" />
<parameter name="videolayeroptions" value="" />
<parameter name="videolayerbuffermode" value="BACKSYSTEM" />
<parameter name="graphicslayerid" value="0" />
<parameter name="graphicslayerpixelformat" value="YV12" />
<parameter name="graphicslayeroptions" value="" />
<parameter name="graphicslayerbuffermode" value="BACKSYSTEM" />
<parameter name="vrect.x" value="0" />
<parameter name="vrect.y" value="0" />
<parameter name="vrect.w" value="1080" />
<parameter name="vrect.h" value="606" />
<parameter name="touchrect.x" value="0" />
<parameter name="touchrect.y" value="0" />
<parameter name="touchrect.w" value="0" />
<parameter name="touchrect.h" value="0" />
<parameter name="pointer" value="false" />
<parameter name="graphicswindowpixelformat" value="ARGB"/>
<parameter name="graphicssurfacepixelformat" value="ARGB" />
<parameter name="extendedaccel" value="true" />
<parameter name="allocmethod" value="malloc" />
</dfbsettings>
If Your X-server/driver does not provide a XV-Port, You should not set the enable-x11 parameter, as the outcome is currently fatal

Maybe this info should make it to the tutorials section...
have fun
Stefan