To preview an avi file splitted in multiple RAR files, you can just donwload the first rar file.

Download and open the first RAR file select the file to extract, right click it, select "Extract To Specific Folder", then at the bottom choose "Keep Broken Files" and press "OK". Now you will be able to preview the first minutes of the AVI file.

Suggestion: let the video play without messing at the "Time Seek Bar", if not, the video might hang and show some squares in the image, but that's only because the file is incomplete.