I created a windows 7 virtual machine on Centos 6 running the following:
virt-install --name=W7VIRT64 --ram=768 --disk path=/var/lib/libvirt/images/guest1-win7-32,size=8 --vnc --network network=default --os-type=windows --os-variant=win7 --cdrom=/root/win7.iso
I was able to successfully install the guest OS and get it to boot.
How do I go about increasing the disk image size to 20G using non-gui tools?