This question was posted in response to the following article: http://help.adobe.com/en_US/premierepro/cs/using/WS03BF7479-8C7B-4522-8C75-210AD102524Ea.h tml
Unfortunately the aspect-ratio setting does not work. If, for example, you have D1/DV anamorphic 16:9 footage that's being misinterpreted as 4:3 and you change it, the thumbnail of the first frame will be corrected in the bin. But if you scrub the footage there or put it in your sequence, it goes right back to 4:3.
This is in CS 6 under Windows.
Correction (since you inexplicably can't edit posts): That's under Mac OS, not WIndows.
OK, WTH? Someone just posted a response asking how I changed the setting, and that response has disappeared.
The answer is: As the Adobe doc says: Right-clicked the clip in the Project tab, went to Modify/Interpret Footage, and changed it there.