Xbox reconfigured to Unix Executable File

I'm not familiar with what an Xbox can (or does) do to an attached drive, but are you sure that the "Dataxxx" files are actually the old files renamed, and not something entirely different that the Xbox saved there? You could do some poking around in one of the files to try and figure out yourself by copying one to your hard drive and adding a .jpg, .avi, .mp3, etc extension (whichever ones the originals would have had) and see if it will open with one of them. If so, you know that they've just been renamed.

Depending on how sensitive the data was/how sensitive you are to privacy issues, you could also try posting a smaller one here for someone to poke around in.

Assuming, though, that the Xbox actually deleted everything and replaced them with its own data, your best bet is to download a trial copy of Data Rescue 3 right now, and see if it can find anything useful in the blank areas of the drive (areas overwritten with Xbox files are guaranteed toast):

http://www.prosofteng.com/products/data_rescue.php

It's probable a professional data salvage service could get stuff off, but it's unlikely they'll get much more than Data Rescue will be able to find, and they're guaranteed to cost at least an order of magnitude (probably two) more.