Forget Genuine Fractals if you have Photoshop, as that does as good a job or even better in most cases. In Photoshop select Image, Image Size, in the box/window that pops up make sure Scale Styles, Constrain Proportions and Resample Images boxs are ticked. The Bicubic Smoother is selected, then just enter a new size in the Document size box or enter a new figure in the Pixel Dimensions box. For example My D3 has a normal file size of 34.5mb but if I increase the Pixel Dimensions from width of 4,256 to 8,512 my file size jumps from 34.5mb to 137.9mb and the resolution remain at 300ppi. This is bigger than A2 and triple the Pixel Dimensions take it to 310.4mb and over 4AO size. All you then need to do is apply a little sharping and it is ready.
Remember, most large images are viewed from a distance and not up close, so this allows you to view the full image in the whole.
