We're only guessing on the depth and speed of the water here. But, from what you're describing, this is pretty tough water to start out on!! Nonetheless, there's a good probability that fish are in there. They don't like to buck the current, so they'll hang in those pockets of slower water you see behind the boulders. Sometimes there is a cushion in front of the boulders they'll hang out in as well. They'll dart out to the faster water to grab something going by and then duck back into their pocket of slower water. Also, watch closer to the stream banks. Often the water closer to the bank is slower than the water towards the center. Fish will hang out in the slower water that's closer to the bank and feed right on the edge of that seam between fast and slow water. It often pays to make your first casts along that 'seam' before you go splashing around in the stream.
Finally, even fast water, if it has a little depth to it, runs slower on the bottom. Any rocks and obstructions on the bottom will give a fish a place to hang out with out needing to fight the current. Get a nymph or wet fly down there on the bottom where they're hanging out!
As far as your other 2 questions: without a lot of elaboration, a leader is tapered so it will cast properly. There might be certain situations where you could use level mono (off a boat for example) but generally you'll use tapered leader so it turns over properly. Secondly, while there are exceptions to the rule, a dry fly generally drifts right along with the current - just like a real bug floating on the water would. At the end of the drift, you'll pick your fly up (with the rod of course! Ha!) and flip it back up stream for another 'drag free' drift.
I'm sure you'll get some other really good info from others on this site that are more knowledgeable than me, but it's midnight and I was in a typing mood!
