Any solutions for when md5 is not present on the device?
For whatever reason, it doesn't appear to be installed on my Droid.
I am not sure why the sdcard would be mounted as R/O. Apps constantly use the sdcard, and with it mounted as R/O those apps would have issues. So a shot in the dark here, but maybe you could use Root Explorer to browse into the sdcard and see if the top right hand button says mount as R/W or whatever it says (my wife has my phone right now feeding her Angry Birds addiction).
Alternatively, I don't see why you couldn't just use a computer to create the MD5sum. I don't really have any advice for this one though. I know I did it a few years back using a distro of Linux, don't recall the distro, but I would imagine both Windows and Mac have options available too.