I am working in compositor and VSE and find that Blender does not seem to understand image-sequences named like 120311_115058__001.jpg? What are the rules for naming img-sequences? Thanks
There should be no issue with such naming. As long as the end of the file name is that of the sequence, for exqample: xxxx_xxx_#### in which # stands for the frame number.
If you are importing into the VSE make sure you select all of the frames that are part of the sequence (press A).
As for the compositor use an Image Sequence node you just need to select the first image in the sequence. Then enable Match movie length and Auto_Refresh.