I had that adventure yesterday:
I installed kernel 126.96.36.199 (test26.s) from slackware current and the newest
ATI drivers fglrx_6_8_0-8.25.18-1.i386. I got error messages about the kernel modules.
They werenīt compiled with the same compiler version the kernel was made.
So I temporarily installed gcc 3.4.4, ran the ati-installer again and everything works fine now.
No recompiling of the kernel was nessesary. (BTW, itīs a Radeon X800 GTO here)