I wrote an script to convert Rackspace Cloud Server Images to OVA files. This file can be imported to Vmware and Virtualbox (and may be other hypervisors).
You have to get a copy of .tgz files generated from Cloud Servers snapshots and then provide it as first argument of this script.
The script is here.
In the comments you can see the requirements and how to use it.
Feedback is welcome.