www.gamefaq.com ---best walkthroughs on the net. I only use them when I'm really stuck, but I'm glad they're there when I need them.
I've got the gang war thing pretty much down though, if anyone needs some tips just shout.
When throwing the boxes off the train you've got to account for movement just like you would in real life, so if the car is next to the train aim just ahead of the guy to catch the boxes, and remember that just like with grenades the longer you hold the circle button the farther your throw the boxes...that's where I had the most trouble.