No longer able to play avi with ...

I have an iMAC that I bought with Snow Leopard installed from the outside and a MacBook Air, which was upgraded to SL. Both machines have perian, VLC, and Flip4Mac installed. I multiple .avi videos that were created with a Microsoft Video 1 codec. These videos play without problem with Quicktime 10 on the iMAC, but cannot be viewed on the upgraded MacBook Air in QT. I already tried reinstalling the OS on the MacBook. Any suggestions?

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