I'm going to be making a large print from a relatively small original (2592 x 2592 px crop from a D200 to a 36" x 36" print, or more exactly 54 4x6 prints that will be assembled into a 36x36- it's complicated but irrelevant). The actual resolution at that size is 72 dpi, which isn't exactly "high quality." I did a test print of a crop from the original at this resolution, and it does look good enough for the purpose, but I'd rather upsize it myself than let the machines at the print shop do it for me. I know there are different methods and algorithms to do this, so I'm wondering what has worked for people in the past. I have GIMP and Photoshop (and yeah, I prefer GIMP for most of what I do), and I'd be willing to try other software as long as it's free. It's really not worth going out and buying something for. The picture, if you're interested: I wanted something ghetto for my apartment, and this was (a) the right color range, (b) square and (c) had some hope of getting to 36 x 36 (sorry 35mm).