Ok, the simplest way to texture this specific model would be to apply a box unwrap. So what you do, is load the model into LithUnwrap. Click "Select" then "All". Then hit "Tools", "UV Map" and "Box". It'll pop up a dialog. Just take the defaults. You should now see your model "unwrapped"... Click "File", UV Map" and "Save". Save the UV map image off to a file. It'll again pop up a dialog, just take the defaults. Also click "File", "Model", "Save" and save your model as a .lum file.
Now, go find the bitmap you created and load it up into your favorite image editing software. Take the image of the gun and make it fit over the unfolded sides of the gun. Find or manufacture a suitable texture for the other parts of the gun and paste those over top of the other parts of your unfolded gun. Save the new version of the bitmap.
Go back into LithUnwrap and load the model back up. Now, over in the right hand pane, double click on the texture entry. That will pop a dialog. About halfway down there will be a drop down list. Click it and select "Bitmap". Then click the "Properties" button. That will pop a dialog where you can load the bitmap you just created in your image editing software, so do that. Now close all the dialogs by clicking ok.
Now you can preview your model and enjoy the fruits of your labors. At this point you can export the model to a .X format so that it can be used in DBPro or Classic... Just make sure to save it as a text file with compression off (those work best).
Intel Pentium 4, 3.4GHz, 1280MB RAM, NVidia Quadro FX3000/256MB, 240GB HD, XP Pro