ok, two separate problems here;
chloe - I assume you know how to program both your computer and the MCU that you are using.
Next you have to choose what kind of interface you're going to use.
As aljamri has mentioned using a plane old serial port is one of the easiest ways to do it. Using the parallel printer port is another, though it's a bit old hat to use parallel comms these days.
I would think that your complier has serial port libraries as does the MCU compiler your using and that you should take advantage of these and read up on them or look for some example code for each end.
The libraries may not define any kind of protocol standards and you will have to develop your own for talking to the device of your choice if such a thing is required.
There are also probably libraries for USB serial communications which aren't that much more complex to use than standard serial routines.
@jemich; download the datasheets for your LCD or a generic hitachi LCD module and read how to initialise and talk to it. Writing the code to handle it will then be very easy.
