If you run the XEN Kernel of SLES 10 and try to change your lan settings
with Yast it will simply shoo you away:

A XEN network Bridge was detected.Due to renaming of network interfaces by the bridge script, network interfaces should not be configured or restarted.See /usr/share/doc/packages/xen/README.SuSE for details.
Unfortunately the readme does not really tell what to do.

Here is what I do:

switch off the XEN network bridge:

#/etc/xen/scripts/network-bridge stop netdev=eth0

Run yast (do the changes):

#yast2 lan

Switch the bridge back on:

#/etc/xen/scripts/network-bridge start netdev=eth0

This of course does imply that

• All VMs are switched off (or they will loose networking)
• Your only bridget network is eth0. (default) Use:
  #/etc/xen/scripts/network-bridge status
  to see how your configuration looks like