what a night! i was trying to expand the size of my spacewalk kvm guest and instead messed it up and so i had to try and fix it. i dint have any luck but i did learn how to take a working kvm guest image and make it bigger.
first of all prepare your host by installing the following
yum -y install libguestfs-tools
next make of a copy of the old guest for the new guest. if you are using this method to expand your current guest, you read right, you will need to make a copy first
cp OLD.img NEW.img
then resize the new image to your desired size
qemu-img resize NEW.img 20G
and now, tell qemu to modify the lvm within the image using the old image as a reference
virt-resize --resize /dev/sda2=20G --LV-expand /dev/VolGroup00/LogVol00 OLD.img NEW.img
finally startup the vm guest and log into into it to do a
resize2fs -p /dev/VolGroup00/LogVol00
and thats it you are done. you can also verify with
df -h
resources: http://libguestfs.org/virt-resize.1.html