I have a similar problem, despite the recommended version of Quick Time (7.7.1), BIAB report error and say QuickTime is not installed, then the audio is apparently re-rendered using an alternate method and get frozen, or sometimes it step to "Rendering video 1 of 1" and still that way forever, finally I have to close BIAB. the problem is present in windows xp (sp3) and the same in Windows 7 SP1. I hope that next build fix it.

Oneil