INT 66 - PenDOS - PKEYUS - SET ???                                              
	AH = 41h
	BX = ???
	CL = ??? (08h-20h)
	DL = screen column??? (<= 50h)
	DH = screen row???  (<= 3Ch)
Return: AX = status (0000h successful, 0001h error)
Note:	this function also sets an internal flag
SeeAlso: AH=42h,AH=43h