kernel 2.6 X11 and radeon M7500

[debian]

Has anyone else experienced problems with kernel 2.6, X11 and radeon 
M7500 graphics card?
when I boot 2.6 everything goes ok until X11 starts, then the screen 
just blanks. no errors appear in XF86 log either.
any suggestions would be appreciated.

on another note:
what sort of frame rates in glxgears would be considered good?
currently I get about 350-450 frames per second (kernel 2.4.24, X11 4.21 
KDE 3.1)

cheers,

Ben.