May I suggest solving this problem with User Mode Linux? This allows you to create a very tightly controlled environment which you can duplicate exactly very easily with (AFAIK) no way out of the controlled compartment. On the outside you can easily block attempts at network traffic, limit CPU usage, protect yourself from using too much memory, disk space, etc. But from the inside it looks like a normal machine..

BTW there are a number of gotchas with Safe. I have found that interesting code (eg stuff that uses Exporter) tends not to play well with Safe...