Note that I've used bridging for the QEMU/Visop setup. This may not be very secure, so don't do it on a live (internet connected) instance.
For the curious, this is how to quickly bridge it all together on a Linux machine:
1) I add a bridge:
brctl addbr br0
2) I may or may not want (optional):
dnsmasq --interface=br0 --bind-interfaces --dhcp-range=172.16.1.20,172.16.1.254,12h
3) ip tuntap add dev tap0 mode tap
4) ip link set tap0 up promisc on
5) I add tap0 to the bridge:
brctl addif br0 tap0
6) brctl show
7) I add eth0 to the bridge:
brctl addif br0 eth0
8) brctl show
These settings are not persistent (AFAIK) - so a reboot takes my system back to "normal" (hopefully). Note that I'm using Gentoo, so the action of these things may be different on other distros! Also, I've just started using Gentoo, so am not really a Gentoo expert either. Thus, this is not advice. Bridge at your own risk! There are other ways to do the QEMU networking, but the bridging method is easier. It's not the best way - but it is the easier one.
When Visopsys runs, it will be able to grab an IP address when I execute the "ifconfig" command, and then click on the "Enable" button.