UV Unwrap and Texture Transfer
You will need Blender 2.46 to complete this tutorial:
My blend file with all views made for you:
1. Download and open my blend file or open blender and make a window for the outliner, UV/Image Editor, Buttons, and 3D view.
2. Import the obj file that you want to have new UVs with Clamp Scale set to 0.
This can be a low polygon version of your orginal model. Meshlab's quadric edge collapse decimation is my prefered method.
3. If you can not see your object hit shift C to center in the view. Left click to select your object. Hit Tab to go into edit mode. Hit U and select unwrap (smart projections).
The default options should be sufficient so click on ok.
You should now see your new UVs layout in the UV/Image Editor window.
4. In the UV/Image Editor click on Image then New. Here you can set the size of your new blank texture. When done click OK.
5. Import your original textured David obj file with Clamp Scale set to 0.
It should automatically be placed at the same location as your first obj file overlaping it perfectly.
6. Using the outliner window select the original object then shift select the obj file that you applied the UVs to.
Hit F10 to go to scene. Under the Bake tab set Selected to Active and textures to on. Turn Clear off. Then click on BAKE.
You should now see the texture placed correctly for your UV unwraped obj in the UV/Image Editor window.
7. You can now select the david textured model and delete it and work just with the new UV unwraped model.
8. Save your new texture file by clicking on Image then save as... in the UV/Texture Editor window. Chose a name and location and click Save Image.
You should save in the same directory as the obj file.
9. You can go into texture paint in blender or export your model to another application that supports texture painting.
I use Maya because unfortunately blender's texture paint will tend to overspray the paint to other UVs and can cause you to paint in two different locations at once. Maya does not have this problem. You can now paint over the magenta triangles!
10. Save your texture file after any editing and export your model.