If you are looking for a free software for the thumbnail .jpeg images of your avi files in the computers,I recommend you a free file management application:file extension ppt ,It can be used in any Windows Version (including Vista) ,I guess that most of us use these operating systems.^_^ We can have all the thumbnail images in the future only if we used it once! On the other hand, we can label our picture in the computer so that we can link back to the original and full avi file.
Of course,It has some little flawness ,but it may not affect us.In a word ,Flie extension ppt is a wonderful tool for our images in the comptuter.
Now this tool It is all for free, and you can download it here:http://www.ifileextensionppt.com/
Important of all it is 100% CLEAN ,NO SPYWARE,NO ADWARE and NO VIRUSE!Why not have a try?