Is there a data recovery software that can detect and join fragmented files?

Try this: http://download.softpedia.com/software/multimedia/video/avipreview_by_aj_026_alpha.zip 

its free.

or check out the page first :

http://www.softpedia.com/get/Multimedia/Video/Encoders-Converter-DIVX-Related/AVI-Preview.shtml

This came with Kaaza Lite once, for watching partially downloaded files.. should do the trick! It will NOT however, restore the files, only show them.

Try this: http://www.download.com/DivX-Repair/3000-2140_4-10502222.html?tag=lst-0-2

aslo free, but only for divx

This: http://www.repairvideo.com/index.html <- top one.. not free, but give it a try!

File fragmentation is not corupt files, if you beleive this is your problem defrag your drive http://support.microsoft.com/default.aspx?scid=kb;en-us;314848

The best I've ever used http://www.ontrack.com/

Saved my @$$ a few times, excelent data rcovery.

http://www.softpedia.com/get/Multimedia/Audio/Audio-Convertors/All-Media-Fixer.shtml

Check this out to fix media files

You can try Spin Rite 6.x -> http://www.grc.com/spinrite.htm
I had a failed hard drive corrupted OS, I ran this tool and took care of things.