A very good source venue for discussing sig2dat and other Kazaa technologies can be found at
http://www.fasttrackmovies.com/
Sig2dat is in the same family as eDonkey. It creates a hash set for each file so that it is unique. Though this site goes into a little of what allows for great video and sound compression it main contains information about creating the hash sets and shows you some hashes that are already available for testing purposes.
According to the DMCA some of the received content, if you wait long enough is considered illegal, be forwarned.
Regards,
Cyberion