I will be quite happy with a software trigger - as long as it’s properly implemented.
As for SD cards - I’m still not able to capture anything even with the files you sent (the files remain binary identical before/after save with M button). No error message is given during save and name advances to next number. Also you did not post a reference to the image utility.
I checked the card, and it is a SanDisk 2GB. I had another brand new card (exact same type) and when I connect it to Windows XP first time (using DSO Nano), it is reported/identified as a 4GB card. Also I tried the DSO/Nano on Ubuntu and the issue is the same - it is not correctly identified. Is there a way I can get the SD card to work for data capture with the DSO Nano?