pan0 is, if I'm not totally off, Bluetooth-related.
virbr0 is VM-related, as it is established by LibVirt.
As said, try virt-manager, it'll be a lot easier.
I guess you're working in a GUI, right?
Ever since I switched to Fedora I used virt-manager, because I was simply sick of having these damn long command-lines for QEmu all the time.
As an alternative you can have what virt-manager offers you in the shell, using virsh, virt-install and so on.
Edit: Just tried this (as root):
qemu-kvm -net nic -net tap,script=no -cdrom Slackware-12.1.iso -boot d
And it does create a device tap0.