Gallium will support r300 Radeon cards perfectly fine. If any I have this for some MESA and Intel video cards at ~/.drirc.

Adapt it for your radeon driver. The device driver might be "ati", "radeon" or "radeonsi".

    <driconf>
         <device driver="i915">
         <application name="Default">
         <option name="stub_occlusion_query" value="true" />
         <option name="fragment_shader" value="true" />
         </application>
         </device>
    </driconf>