AE sets PAR ratios based on frame size. By default NTSC DV(720 X 480), NTSC D1(720 X 486) and PAL D1/DV (720 X 576) frame sizes are set to a 4:3 picture aspect ratio because the majority of footage at those frame sizes are not widescreen. There are other non-square PAR frame sizes that are automatically assigned their own PAR. These include HDV, DVCPro HD 720 (1440 X 1080 or 960 X 720) or DVC Pro HD (1280 X 720).
Universally it is easier to work in AE if you use the square pixel equivalent frame size for your project for all of these formats. Only D1 or DV frame sizes routinely misinterpreted as 4:3 or SD picture when the footage is actually widescreen. For every standard frame size listed, if you create Photoshop images or crop images to those frame sizes the PAR will most likely misinterpreted as non square pixels. The only way that you can create a Photoshop image that is not square pixels is to use one of the non square templates or intentionally change the PAR of the image. Every graphic you create in Illustrator with a standard nonsquare frame size will be misinterpreted as rectangular pixels. It is not possible to create a non-square pixel project in Illustrator.
That said, and to get to your problem, the PAR interpretation rules are contained in a file called interpretation rules.txt in you CS5 AE root folder. This file can be edited to interpret you DV footage as widescreen so you don't have to go back and change it every time. If you're rendering to most codecs, including DV, AE has no ability to add meta tag info concerning PAR. Many formats do not support this information at all so your only option is to watch for and fix any PAR interpretation rules errors.
I'm not sure where this file in in CS5.5.
If you want to send your files to the internet it is very important that you work in and render to square pixel frame sizes.
I hope this helps.
I see. Thank you for your time and attention.
Thank you very much. It does help.