Question: What is the meaning of, "I'll make a ghost of him that lets me"?
Answer: "I'll make a ghost of him that lets me," means, I'll
make a ghost of him that hinders, prevents me from going.
This word let, though having the same form, is derived from
an Anglo-Saxon verb, different from the word let, which
means to permit. (Anglo-Saxon laetan means permit and
lettan means prevent.)
Mertins, Emma. Shakespeare Examinations. Ed. William Taylor Thom, M. A. Boston: Ginn and Co., 1888. Shakespeare Online. 10 Aug. 2010. (date when you accessed the information) < http://www.shakespeare-online.com/plays/hamlet/examq/let.html >.