For some reason I'm not finding where the discussion was taking place, but there was a thread where we were talking about running injuries and I mentioned an assisted running machine my PT uses.
I was back in yesterday and asked him about it. It's technically called an unloader. It's actually primarilly used for people with back injuries, relieving pressure, herniated disks, etc. More PTs have been starting to use the for running rehab because, as Peter said, how else are you really going to safely go from no running to full weighted running.
I wasn't able to find actual pictures save what's in the article below, but it should give a lot better idea of what I was trying to describe.
The article (pdf document): [URL=http://www.record-eagle.com/sections/2006resolutions/10.pdf]An article partly showing it's use/picture[/URL].