Audio becoming more and more out of sync with the video as length increases is a well known problem when using variable frame rate (VFR) instead of fixed frame rate. If you watch the video Steve posted again, you'll see that he talks about how important it is to select a fixed frame rate and not default to VFR. I suspect those experiencing the sync problem used VFR. Use fixed frame rate and you shouldn't have this problem.
The AVI file you get from capturing with the Canopus/Firewire and windv is fixed rate video too.
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