Hi
Not sure where your "lines" are coming from. What format are your clips?
With regards the blurriness or grainyness seen in the VP preview screen (RHS for the project) I presume you mean pixelated???
VP does not produce a HD preview image. Presumably as it is reduced in size to fit the screen space available this is not necessary. It would seem then that the sequence is compressed and then reduced in size to fit the small screen where it will run at the correct speed.
Like all compressed images where data is lost, subsequently reducing the size "restores" the definition and at the size shown in VP it looks generally OK and perfectly adequate for the user to see what is happening. After all it is only a preview.
If you choose to view the preview using the full screen option it may look more pixelated (or grainy) as VP still presumably goes through the same process but blows the image up to a larger size and consequently the pixels start to show up.
When, however, VP saves your project it has plenty of time to render the video correctly and, provided you have set the correct parameters, this output should look OK.
Nat