Hello Aurélien, hello Wim,
Have you tried some newer 2.6 kernels ? Debian's 2.6.8 is crap for me (It's quite unfortunate that it was shipped in this state) and starting from 2.6.11 it gets vastly better. 2.6.11 kernels are available for sid, so you can easily get one for Sarge (it will work out of the box wrt sid/sarge differences).
I will try that. Thank you. Philipp