There are many programs out there that can reproject an image. If you're using FT3, I recommend the following workflow (which is quite similar to Ralf Schemmann's old Jhendor tutorial at http://www.jhendor.de/tutorials/cc2-ft.pdf ):

1) Use FT3 ( http://profantasy.com/to produce a polar aspect map grid at the resolution that you desire (e.g. Lambert Azimuthal Equal Area projection output to a 4kx4k PNG file Click image for larger version.  Name: LambertAzEqArea_Polar5deg.png  Views: 214  Size: 400.1 KB  ID: 65034 ).
2) Use this projection template as an overlay layer in Photoshop and paint your height map in the background. The extremely lazy among use might just rough it in and use something like the process described in http://www.cartographersguild.com/ma...und-lands.html to finalize things.
3) Use ReprojectImage ( http://www.ridgenet.net/~jslayton/ReprojectImage.zip ) to reproject the world data to the equirectangular projection that FT expects as its binary input.
4) Use Wilbur ( software ) to flip the image vertically and to convert the reprojected image into a .mdr file.
5) Use FT3 and create a new world (File>>New) using the binary mdr file saved in Wilbur.

If you just want to use a picture in FT3 but not height data, you can use the image overlays feature of FT3 to load the output of ReprojectImage directly.