Mouse:
... The data-sheet is not helpful in giving information about addressing the four lines or the memory map layout of the displayed characters.
I have some information about LCD addressing at http://web.alfredstate.edu/weimandn. I am working on an update to include 16x4 displays, but the current info should help you understand the addressing.
By the way, the number of 'lines' that you specify in the initialization does NOT refer to the number of visible lines on the display. It refers to the number of lines of memory used, as interpreted by the LCD controller. The only valid choices are 1 or 2, and 2 is the correct choice for almost all LCD modules (even many of those with only one line on the display).
Don