EciAdsl driver is compatible with 2.6 kernels since version 0.9.
All 2.6 kernels between 2.6.0 and 2.6.6 have to be patched (look at link below).
Update on 2004-06-23: 2.6.7 and 18.104.22.168 kernels are not stable with EciAdsl.
Kernel 2.6.9-rc1 seems stable.
Feel free to report us any stability problem with 2.6 kernels.