you are right, the X1000 desktop series (engineering: r500, supported by driver r300) SHOULD still be supported by the regular mesa - packages
according to this site: https://www.x.org/wiki/RadeonFeature/
r300 already is a gallium-driver, too.
Would you mind posting the output of inxi -Gxxz on the machine?
I suspect that the mobile X1000 is not a real X1000 like on desktop, but an older chip, maybe only supported by r200 or r100. Unfortunately, using older chips for mobile and rebranding them to an officially more modern series is a common practice.