So, I got a really good question about getting started in Dark Heresy. It's not that hard, but it can be a little difficult depending on your friends, and where you live. You need three things, dice, books, and people. Thankfully, Dark Heresy is very forgiving in the first two categories, but like all RPGs that last category is ever illusive. Ideally, you want your friends to be the people, but depending on how receptive they are to such an idea, you might be out of luck.
Dice and books are the easy part. You want at least two ten sided die per person, as you will need to roll two of them at a time. You will need one that counts one through zero, and another that counts ten through one hundred. This combination is abbreviated as the d100, and gives you a percentile score. Popular names for it also include "Percentile dice." When rolling to see if you succeed at a skill, you roll the percentile dice, or d100. If you REALLY want to look, you can find an actual one hundred sided die, but they are silly and not neccesary. For the books, all you need to actually play the game is the Dark Heresy Core rulebook. It contains everything from the player classes, to the rules of gameplay, and scenarios and monsters for the GM to throw at you, as well as setting information. The dice probably cost about twenty five cents each, depending on where you buy them, the book is about fifty dollars but prices change based on where you go, as well. You can find the book at almost any book store, in Barnes and Noble they keep it near the comic books and graphic novels, in Borders I usually see them put it near the anime and manga, or the fantasy novels. Dice can either be bought online, or at your local comic shop.
Finding people is tricky, but if your friends are real bros, they won't have a problem with trying out the game just once. If you make them get into it, they'll come back for more, but you'll bear the mantle of GM forever. Unless someone thinks he wants to try it out, but trust me, that's rare. If your friends refuse, try your local comic shop, if they host RPG games, there might be a group there. Problem is, you run the chance of meeting real weirdos, as well as pretentious people. Online gaming has the same problem, but you also don't have to actually listen to them complain, and you can always drop out without having to face them again. Play by post, IRC, and messenger play are popular, but all require some dicerolling program, otherwise you may as well just freeform it out.
If people are interested, and don't have conflicting schedules, I might run a Dark Heresy game on IRC or something.