Lightroom: Thumbs for video files not playing with QuickTime

We produce AVI videos with a simulation software under Windows 7 using various codecs, mainly x264 and xVid, some in mpeg42. While trying to import these videos in Lr 3 I only get blank screens instead of a preview picture. The video will play though through my standard player. However, its not that useful to have loads of "white" previews in my database as I can't discern them well.

I noticed that if a video won't play in QuickTime (under Windows) then Lr won't create the preview picture.So I tried to find a solution how QuickTime would play those AVI files. The only package I found is 3ivx.com - but it only works for the xvid files, not for any of the other formats. There are other packages available, but only for Mac OS, not Windows 7.

A possible solution for a fix in Lr would be:
If a preview can't be rendered from the AVI file directly, why not use the preview from a sidecar THM or JPG file (which also includes some meta data used for the video like date/time)?

Or is there any other solution to get a preview for AVI files (created with the codecs mentioned above) under Windows?