High Res Images for Pre-Press Printing

[Ashlie]

I have several images at 72 dpi but the actual size of the photo is huge - 36 inches by 20 inches. The photos will not appear larger than 4 x 6 in print. I have been told by a professional photographer that 72 dpi should be fine for print if the image is very large and it's printing at a smaller size. However, the printer disagrees even after printing several of my 72 dpi images in brochures without any problems. He says I must convert my 72 dpi files to 300 dpi which just makes the file size huge! So I am in the middle of the professional photographer and the "professional" printer/graphic designer. Does anyone know if the photographer is correct? So far in my experience, as long as the image itself is large, 72 dpi is ok for print. I am thinking that maybe the printer isn't as knowledgeable as he tries to appear but I really don't know...any advice or input?