What Hai-Etlik says is true. However, for relatively local maps (say, a couple hundred miles across or less), the projection effects are minimal for an Earth-sized world. After you determine where on a globe they should go, you can then distort them approximately using something like Photoshop to get them roughly into place. Unless you're dealing with large numbers of mostly-polar maps, most folks won't notice when you do this sort of thing. If you're aiming for atlas-style maps or have multiiple overlapping source material then things will get a little harder.

As tolcreator pointed out, gprojector is a good tool for reprojecting images.

Many years ago I wrote a toy called ReprojectImage ( http://www.ridgenet.net/~jslayton/ReprojectImage.zip ) to let me convert pieces of images into straight UV textures suitable for mapping onto spheres in various projections. It's a Windows-only toy, however. I have used it with moderate success to warp disparate map chunks into a single projection that then gets assembled in Photoshop.