Here's a small PERL script I whipped up for you that should do the trick...
http://lbbv.com/rename.txt
Upload it as ASCII one directory up from all the files you wish to rename and then run "perl rename.txt".
NOTE: USE AT YOUR OWN RISK. I ACCEPT NO RESPONIBILITY FOR WHAT THIS CODE MAY DO...
You might want to create a create a test directory first and test it there before running it on your 800 directories.
-- Bill