Since the tile editor I had made was full of bugs and I didn't want to continue supporting it. But you can specify any other program you want, like GIMP or whatever, if you check the preferences, file associations tab. On a side note, I'm glad it seems to open Paint correctly on Vista lol... had no way to check, really. Maybe I'll compile the old tile editor we had in its own exe, and make it available for download if people still want to use it. But I strongly recommend GIMP, it's free, and it's not bugged like my editor