I managed to mount the image file, thank you, AndrewS. But just copying the files to the partitions of my sd card will not work, I guess. There are numerous ELF- and BIN files, which have to be copied in a special way.
How do I proceed to install arch from the content of the image to a 6 gig sd card instead of dd'ing the whole image with its only 2 gigs?
Reagrds
poseidon