From Duna's surface you only need about 3000dv to return to Kerbin. Its a good bit but its certainly doable. My advice is just to build big. A two stage lander would probably work well.
Go to the r&d facility. Find the node with the klaw in it and select it. Click on the photo of the claw and choose research. This happens when you add or remove parts (from mods) or move your save to another version.