Ok, after changing the jumpers the network card works, and I can ping other 
computers in the network and vice versa. But as the Acorn SCSI card is not 
supported, I guess my only option is a nfsroot install.

Is that possible? How can it be done?

Can I use a standard installation kernel to install to a nfsroot? But how can 
I tell sysinst to install to a (possibly already mounted) nfsroot? Or can I 
just explode all the sets to the nfsroot?

Once I have installed it, how can I boot the kernel so that it uses the 
nfsroot? How do I pass arguments to boot26? Is there a boot26 documentation 
somewhere?

If nfsroot is not possible, which harddisk interface can be recommended to get 
for use with NetBSD on the R260?

Thank you for your help!
Peter Teichmann