Video preview choppy. Due to intel atom?

It could be, especially if they are HD files. Have a look in the Openshot preferences and the change the preview mode to sdl_preview, that might make a difference. But ultimately, an Atom hasn't got enough power to edit HD files.

Whether the files play ok in VLC is pretty much irrelevant, a video editor will need more resources than a media player.

I'm not sure if it is HD but your idea about the atom makes sense.
I tried sdl_preview, not much difference.
I'm just wondering, if I haven't added anything to video, shouldn't it just play normally, like it would in a media player, why would the preview need more resources?
Also is there no way I could make the video preview resolution lower?

The explanations of Andy are good but it can be explained too by your version of MLT (the Video framework of Openshot) if your are using the 0.7.2.
See here in the section of Ubuntu how to grab the last version of MLT and here more explanations too : http://openshotusers.com/forum/viewtopic.php?f=11&t=974and http://openshotusers.com/forum/viewtopic.php?f=12&t=914 .

Nope, not 0.7.2 just 0.6.x (x is whatever)
I think I read one or both of the links when you posted this but at the time of writing, they are both dead.

Yeah, we have yet attacked and Andy is on. Now, a part of the forum is became. I can not tell you if it is available (I've not checked) but all is not finished. I 've seen two spam and ............I can remove them...... Even, I can not stay login.....