Handling huge textures on a quad to simulate landscapes

Hello !

I’m trying to learn how to handle large textures mapping. I have a huge picture (could be like 5x5 640*480 screens) mapped on a quad that represent a landscape and I would like to be able to scroll around. What is the best way to do this so it doesnt only run on high end cards ? I don’t want any border effect to be visible between tiles if I have to tile my picture… I need to give the user the illusion its just one big picture.