Don't use
cp /mnt/card/pico /bin
This is trying to replace the directory /bin by the file pico, good thing the Zaurus is not letting you do this. maybe you can try
cp /mnt/card/pico /bin/pico
or
cp /mnt/card/pico /usr/bin/pico
But if you copied it to your home directory, using the first command I suggested you can run by typing
./pico
Felipe