View all video files as thumbnails in Windows XP

Registry Tweak(A simple tweak)

While in thumbnails view in explorer of Win XP, we can see video's starting frame but only for some of the predefined video file's extensions like mpg, mpeg, avi but not for extensions like rmvb(Real media files) and 3gp & 3g2(Mobile video files)
Here we will just copy the settings of one extension to another through registry editor and we will be able to view their first frame in thumbnail just like as we are able with pre-defined files.
Note: Registry should be handled with care, I would recommend taking a backup before you do any changes in the registry. I don't take responsibility of any damage or loss incurred by users while implementing this tweak.
Steps For Doing It:
1> Open Registry Editor (By typing regedit at the Run prompt)
2> Select HKEY_CLASSES_ROOT and find .avi (any of the mpg,mpeg will do)
3> Export its registry settings (will be saved as *.reg)
4> Right click on *.reg file and select Edit
5> Now if you want *.divx files to be treated in the same way as *.avi files then just replace avi by divx in the file. Save it and execute it.
6> Repeat Step5 for various files of whom you want to change the behaviour.

Note:This doesnt work for *.vob files.

source: here