Thanks all,
I tried to find the newest debian kernel source on one of the mirrors.
(My NIC is not recognized; so apt-get install won't work).
The one I found was 2.6.8
Installed the source and could compile sk98lin succesfully.
My screen froze when I activated eth0.
Reboot ended in kernel panic:
eth0: network connection up using port A
<snip>
Kernel BUG at net/core/skbuff.c.91!
<snip>
<0> Kernel panic: Fatal exception in interrupt.
Well, I guess I have to compile and install a new kernel-image with PCI-Express enabled before I compile the NIC-module
Any (better) idea is much appreciated.