So I've been messing around with some games and one game I came across stores some of it's text in two lines of 16 tiles a piece. So anyway, I was wondering what would be the best way to go about replacing it. I probably wouldn't have enough room to just put english letters for each tile. I'm assuming that I would want to create some graphics, but I'm not really familiar with any programs or specific features that do that.

Also, every time I change something in the game, most of the graphics are replaced with 0's. Anyone know why that is? I think it might have something to do with the checksum, but this is the first time something like this has happened to me on the NES.