Ok
here is how kvm templating currently works in pve
http://pve.proxmox.com/wiki/VM_Templates_and_Clones
basically, it is supposed that you create a template _in_ pve from a working VM. Once you have a base VM, then, you convert that to a template, and you can then "clone" from that template.
so, afaik, you could create a new VM with a fake small disk (qcow2), then stop it and use pve shell to replace this (with the same name) with your image in the same format. after reboot, you shoud be able to boot your staklet vm.
if this works, you can convert the VM to a pve template and use it to clone other VMs (see above link)
it should work...
I dont' think that /var/lib/vz/template/qemu/ is involved, atm. I have templates and clones, but that folder is empty. base images are in the usual kvm folder, as regular images, but they are used as "golden".
[edit] you can also use vmdk/raw images, but templating in pve works with qcow2, so you will have to convert them to qcow2 before, in that case, with storage migration feature...
Marco