Read the section here about PNF stretching: http://www.cmcrossroads.com/bradapp/docs/rec/stretching/stretching_4.html#IDX102
Give that a try and see if it improves your flexibility.
On the whole though, I think that the more you improve your bodily alignment and balance, the fewer problems you will have. I have basically the same problem as you - extremely tight hammies - which in turn has lead to slightly rolled in shoulders as a compensatory response. That has also led to extrernally rotated knees (and resulting knee injuries). Where I'm going with this is that one link in the kinetic chain can throw things way off. By concentrating on correcting your hip and hamstring tightness, you might be able to correct other existing problems and prevent future ones. Pete Egoscue has made some decent progress in these areas, although I think there are better methods than his "e-cises" out there.