The guest is set up to get its configuration via dhcp, alternative it is
assigned the address 10.0.2.16 (instead of 10.0.2.15 if dhcp would have
worked). Obviously the traffic into the guest fails, where as the traffic out
of the guest works (see the "info usernet" output). This is also shown in the
status window of the lan connection. I can see outgoing packets, but no
incomming (at least with the pcnet card, with the rtl8139 I see the
connections in the qemu-console but in the status window of the lan connection
within xp there are no in/out packets counted). Obviously the network card has
an influence to the (partial) working, so I tried the virtio card. No change,
still just outgoing packages :-(
No to both. The traffic goes outside properly as we can see from the responses
of the printers to the question on the 1900 port.