ok, even after you run virsh, you still have to connect to the local machine to undefine it:
virsh -c qemu:///system undefine c
but then something is wrong with my setup I'm using the create a new domain with virt-install, this tries to create another domain named 'c' for some reason, I'm betting it's due to a deprecated switch of some kind, possibly on the .iso source location, so I'm trying:
virt-install --connect qemu:///system --name sq3 --ram 1024 --vcpus=8 -f /home/vm/vm14.qcow5 -s 100 --location=http://ftp.us.debian.org/debian/dists/squeeze/main/installer-amd64/ --vnc :2 --network=bridge:br0 --hvm
but that gives me the error:
ERROR operation failed: failed to retrieve chardev info in qemu with 'info chardev'
I'll post if I get it working. In the meantime, just use Debian Lenny, it's far easier, I needed Squeeze because Lenny didn't have my NIC drivers for a HP DL180 G6 and I didn't want to compile them, they are part of Squeeze though.