INT 16 - PCIBM PC Tools v5.1+ BACKTALK - INSTALLATION CHECK
	AX = 6969h
	BX = 6969h
	DX = 0000h
Return: DX nonzero if installed
	    BX = CS of resident code
	    DX = PSPsee Program Segment Prefix segment of resident code
	    DS:SI -> ASCIZA NUL-terminated ASCII string.	The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h.  Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. identification string "CPoint Talk"