This helpful
thread by Computerex gives alot of useful links for those who wish to envolve themselves in addon development. I find things hard to read myself, but enjoy learning through trial 'n' error, mostly error. But you'll find most of what you want there.
In regards to cargo's...
I used "Wehaveaproblems" XR5 CargoTemplate which you can download [ame="http://www.orbithangar.com/searchid.php?ID=3623"]here[/ame] and I used it for the XR5 Umbrella cargo. But when you install it, just transfer the file from Orbiter\Config\Vessel to Orbiter\Config\Vessels, otherwise the template won't work. But once you've read the pdf a few hundre3d times and mastered the basics, you will be able to adapt it to other cargos, like the XR2, DGIV ect. The concepts are the same. Just ride the frustration and hide the hammer, computers are expensive.
Vessel Skins...
If there's not a repaint kit for a skin, convert an original dds file and edit it like you've done for your cargo, converting it back to dds. To convert bmp, jpg, png and tga to dds I use this
converter. It's idiot proof, so I love it. If you notice windows in a skin, like the one on the XR5 skins I released which weren't originally there, convert to PNG otherwise bmp, tga ect will fill the windows in a base colour when you convert back to dds.
If you require help with your art work, just pm me what you've done, any format and I'll have a go and return in the same format. Please provide any images ect in links and explanation to assist.
Other than that, this is all you need to start off I think, unless others can add to it.
But don't worry about pm'ing me. It's never a bother m8. :thumbup: