In general, the vesa driver will work for most setups, so the model should not matter. Xorg will attempt to use the best suited driver though. To use a configuration file, it should be /etc/X11/xorg.conf - there should be some details in the .info.
Try the usual X -configure, then manually edit the display driver to have "vesa" (autoconfigure should have your busID automatically saved too).
Side note: the gfx chipset core appears to be a rv620, which is not a r700 (which are currently only discrete, and imply something along the lines of a radeon 4850/4870 X2 - EDIT: those appear to be supported by the radeon driver). It probably came out after this Xorg release, which is why the radeon driver does not recognize it.