You could to back to Dallas, November 1963, stand on the grassy knoll and shout "duck".

I'm so glad you posted this. Red Dwarf FTW.
I wouldn't want to go into the past too much because I would know so much of what should be happening, it would be pretty wierd. I mean, it would be cool exploiting everything and investing in all the companies you know will skyrocket, etc, but it would feel too much like Ground Hog Day. I guess everything has its price.
And if you go back really far, you would have a different immune system then everyone else and likely kill them, right? Just like when Columbus and his crew came to America and gave the Indians small pox...and gonorrhea, though thats different. Though perhaps the Time travel salesman can get you a good deal with the immune system faerie.