earlybird1uk,
You can preview your movie (even if it's a .avi), providing your player has all the necessary codecs.
Look up the file with Bitzi before download. When your search results show, right click on the file > advanced > look up file with Bitzi. If Bitzi has a bitprint of the file, people may have rated it & you can see whether it's a good version/junk/porn etc. If the file's not rated, you take your chances.

The stickies around different forum sections are worth reading. They have lots of info & answers to the most common questions.