i got mine to work by installing different drivers. the ones that worked for me (Ati Mobility Fire GL T2 128) was the ATI Fire GL T2 drivers, i.e. the NONE mobility ones.
Man, i have had the roughest time with EVERY ati card i have ever owned, and have never had a problem with Nvidia, ever. I would never spend money on anything ati, and i advise that you all do the same.
(the only reason i have an ati carded laptop is because it was part of the school i'm going to, otherwise, i wouldn't have it,