re: Alexander the Great coins
Most of the territories conquered by Alexander were divided amongst and administered by his generals (the Hellenistic Empire). Egypt, for example, was run by the Ptolemys (not the astronomer Ptolemy, it was a common name in those days). Cleopatra was Greek (Macedonian, actually). I don't know how long Greek/Macedonians ruled in Afghanistan after Alex's death, but perhaps those coins date from that era. Is there any writing on them, can you read the alphabet?