INT 16 - PC Tools v5.1+ DESKTOP API - CREATE/OPEN/DELETE FILE
        AX = FFD4h
        BH = 3Ch create file (with no attributes)
             3Dh open file
             41h delete file
        BL = access mode
             00h read only
             01h write only
             02h read/write
        DS:SI -> ASCIZ filename
Return: BX = file handle
            0000h on error
Note:   operation is attempted in (in order) the directory from which the
          desktop was started/run???, the directory specified with the
          filename, X:\PCTOOLS\, and X:\