Flight Plans.

I recently purchased PMDG 737 NGX,love it.I have entered the two tutorials flight plans and they were a success,but any Flight Plans I downloaded from the internet something or other was not working with these plans.I did enter sids and stars but cant make heads or tails of them.Is there anywhere I can get flight plans that come with sids and stars if a runway was nominated,or must I devote time in study,I like flying sims but don't like having to spend many hours trying to get a flight  plan loaded when I prefer to spend the time flying.

Appreciate any suggestions.

Mick.