I guess the question is how quickly do you wish to update the display. The method Henri described would be quite slow. concidering that you have 3 bytes of data to write to just to address one memory location. As normal with me, I haven't read the data sheet, so what follows is verbal garbage, and theortical stuff....
If each memory location stores a fully byte, 8 pixels either horizonal or vertical, then 640x480=307200, Divide that by 8 for the 8 bits of pixels per write, =38400 and then multiply that by 3 to get the data writes to achieve the full screen write, =115200. Ok.. So thats that data bytes needed to be written out of the LPT port per screen. Someone said eariler that the LPT port is capable of 2Mbytes/s transfers? Cool. So, 2097152/115200= just over 18 frames per second.
Seems acceptable to me, for a data display anyway. Although I would hate to see the CPU usage for it Concidering that doubling the size of an LCD Quadruples the amount that needs to be processed. Sure, if the Computers main task is to display that data, then CPU usage isn't a problem. But if displaying that data isn't a priority, then you really have to ask yourself if it's necessary to have such a large display.
However... standard disclaimer... Everything above was thoeretical crap, done without even reading the datasheet...