Hi Gomo,
Combustion does display the pixel asp[ect ratio for an image when you enable the vuewers to do so.
Firstly you need to se up the pixel aspect ratio for the footage and the composition.
For the footage, expand your layer and click on the "Footage" node. You will find two sub-menus and there will be an option to set the pixel aspect ratio. There are presets for everything you need.
As for the composition, select the "Composite" node in the workspace panel and select "output". You then set up the aspect ratio for the composite.
Once you have set these settings then right-click on the viewport and enable "use ASpect Ratio" and your image will be displayed correctly.
The reason for setting up pixel apect ratio for each part of combustion is that it allows you to mix footage with different different aspect ratios together and output them to what ever format you desire at whatever pixel aspect ratio you choose.
Regards
Grant
DISCREET UK