unix command line tool <find> and compare the first line of data?
geektest: write a one-line perl script to do the same?
there's an OS X utility called Filebuddy that could do fancy finds (e.g. find files of same byte length, or whaterver and case save the various find 'settings' - maybe there is similar tool for XP/W2K
the standard OS X find tool has abiltity to find content - but is limited to text strings
it sounds lo-tech, but find <all> files sorting the output by byte size. you could restrict searches to .mov or .avi or .divx to speed up manual process of searching results file.
get Portfolio for PC (is a digital asset manager tool forimages, audio, video, artwork etc), load your drive into it, then start searching and finding various bits of media.