...and a few moments later I was able to fix it myself!
For others with the same problem:
I found Linux drivers on the network chipset manufacturers homepage:
http://www.marvell.com/drivers/drive...?dId=107&pId=9
I ran the installation script, simply chose "Installation" and a new kernel module "sk98lin" was created.
I added it with "modprobe sk98lin" and the network was finally reachable.