You might find Spring.NET's AOP support useful. I've used the Java equivalent, but not the .NET version. It allows you to instrument existing code to add functionality such as you describe, without having to change the existing source. I don't really like AOP but it can be useful for situations like this.

Look into the PictureBox control. The Image property should be fairly self-descriptive, and Image.FromFile will give you the image itself. However, this will lock the file - if you don't want this effect, use Image.FromStream instead

To ensure backward compatibility with VisiCalc you'll need to have the option to display negative amounts with the minus sign following the number. Of course, you'll also need to make your app run on CP/M. ;) "A Journey of a Thousand Rest Stops Begins with a Single Movement"