Watch the Oregon online guitar lesson by Stephen Bennett from Harp Guitar Repertoire
Note the fingering of the initial D chord. If you're not used to playing this fingering of it, you should get that way. It's the best way to make certain things happen, including what you need for this tune!
Do nail the first phrase of the tune before going on. It will feel good to be able to do so and it will feed your need to learn more!
Be sure to absorb what I say about how you've got the 3 different endings to the initial phrase.
Also - the bit where I talk about how the addition of the B sub-bass string to the ordinary D chord form creates a new chord of Bm7 - that is an important realization to have about the harp guitar. If you maintain the plain old D chord on the guitar and play a G sub-bass, you have a Gmaj9. Play a C sub-bass with the D and you have a D7/C (a D7 with the 7th in the bass). The point being that you can get some mileage - in your compositions and your arrangements - out of this idea.