Setting up xen instance using .tar.gz image

Hi,

I'm new to using Cloudmin 5.7 I've happily created several zen instances using the downloadable images without problems and they run as expected. The documentation that i've seen says you can use a .tar.gz of a working system to install a xen instance but nowhere can I find how to do this and googling doesnt suggest how. I need if possible to load a .tar.gz image into a new instance because I want to explore using elastix under zen and the image that I have been supplied with as a preconfigured solution is only available in that format. Suggestions as to where to look or how to install a .tar.gz image very gratefully accepted.

Thanks

TimLovell