There are a lot of fake files being spread around on the network. This includes audio as well as video files. More info on fake files in this link:
Recognising Fake files
One thing you can do is check the files with
Bitzi Web Lookup before attempting to download them. If noone has rated the file there's a pretty good chance that it's a fake. Then preview the file when it gets to about 15% completed. That way you don't waste you time downloading a dud/empty/renamed porn file.
You can also search for files in bitzi and use the magnet links to start the file in limewire. See:
How to use Magnet Links & Direct Connect
Also if the video is very new it may not be on the network yet or may only be a poor quality cam version available. It takes time for files to filter through the file sharing networks.
This thread has good tips to help improve the success of your file searching.
How to find music. Also applies to videos.