If I hadn't seen it myself, I wouldn't have believed it. Surely you can't get a quality 30" x 20" photograph from an old 8 megapixel dSLR? Well you can, with a little help from your photo editing software.
The trick you see, is to resize. I ordered this Photo Poster from Photobox, and duriing the selection process the site warned me that my image was too small. I opened up the image in Photoshop, but you could use Elements, Lightroom, The Gimp, or most other eding tools, then resized it to 30" by 20", saved it as a high quality jpeg, then tried again at Photobox.
Photobox was happy with the quality, so I uploaded the image, and a few days later I got the poster print in a tube. I opened it up and was very, very pleased. It was slightly dark, but that was my fault, next time I'll make the image slightly brighter.
So you see, the next time you take a photo you really like, resize it, then print it big!