Nice introductory article but I think it is for printing on billboards, paper and posters. Principles are essentially the same though but I felt that the article ended abruptly.
Usually 200-300dpi is used for printing on transparencies. It is true that working with a document in its actual print size and the proper dpi is best. However, I disagree with the blanket statement "As we know, resampling a document up is bad". All is not lost if the customer wants to enlarge the printed image. Don't be afraid to experiment if necessary. Resize and resample upwards if you have to. Unsharp mask can help but play with the gaussian blur and some resampled images are improved dramatically. Maybe someone can add more advanced tips to the thread