I have had good success with photorec, but it will take a really long time to run (like a week or more). It's meant to get anything salvageable off a corrupt compactflash card.
Testdisk will sort through partitions looking for old / deleted ones: most likely won't work here.
I think your best option is to grab anything that looks like a file from the "empty" space in the HDD. For that purpose, DDrescue is likely your best bet. Here's a good howto / article I found pretty quick:
http://www.forensicswiki.org/wiki/DdrescueI only started using this later on a little, so I don't have as much experience, but once I got started with it, it was great. I don't remember if I was using DD_rescue or DDrescue, as I think the debian / Ubuntu repos have it named slightly differently (like gddrescue or something stupid). My method was to boot a light linux image (modified from one called crunchbang, based on debian) to RAM, then load the app from the same flashdrive, but you can just download it and run it normally once you are booted to the live environment. Either option works well, provided you have like 2GB or more of RAM, and depending on the size of your linux distro.