What version of lithunwrap do you have? I have 1.3 which was the last freeware version. Now all you do is open LithUnwrap. Click File, Model, Open. (For this example use the chaingun model because it has no UV coordinates). When it complains about it having no UV coordinates, just click ok and ignore it. The model will load and there will be a small white box in the upper left corner of the client area. That's all the vertices all sitting in one spot. Now click Select, All. The little white box should have turned red. Now click Tools, UV Mapping, Planar. This should pop up a dialog. Click the "Z" radio button, Click the "Top/Bottom" radio button. Then click the "Ok" Button. There you will see the chaingun's vertices all spread out. Now there's a lot you can do from here, but to keep this simple, we'll assume you're done for now. Now, Click File, UV Map, Save. This will save the Image that you now see on your screen to a .bmp file. Click File, Model, Save and that will save the UV Mapping coordinates you just created. Now go open a paint program, grab the .BMP you just created. Using the lines on the image, paint the texture for your model and save it. Then, go into Lithunwrap again. Reload the same model as before. Over on the right hand side is a treeview control. Click the "+" beside "Materials" (if it's not already expanded). There should be just one material, named "blank". Double click on "Blank", that should load a new dialog. Where it says "Diffuse Map", Make "Map Type" say "Bitmap". Click the "Properties" Button beneath it. That should load another dialog. Click the "Change" button on the new dialog. Then load the bitmap that you drew with the texture. Click "Ok" on this and the other dialog. Then save your model again. If you want, you can click Preview, Show Model and see the model rendered.
Attached is conv3ds.exe
Intel Pentium 4, 3.4GHz, 1280MB RAM, NVidia Quadro FX3000/256MB, 240GB HD, XP Pro