You can Increase your Marksman skill by shooting targets.. there are some behind the fighters gulid in Chorrol.. or going to..
If you are a Low Level
Edla Dark-Heart: Bruma (Regner's house on south side)
Shameer: Skingrad (house West of Great Chapel of Julianos)
If you are a Medium Level
Reman Broder: Skingrad (house in South West corner)
Pinarus Inventius: Anvil (not sure where, I think hes walkin around)
Master Trainer
Alawen: Troll Candle Camp (East of Anvil) or he's out hunting
Make sure you have gold, Unfortunitly you can only train a skill 5 times each level.
Yes you can get away with it Kman... It's just hard... Thats what I try to do with the Black hourse courier people lol.. not only are they hard to get with 1 shot 1 kill, but trying to get away with it.
Also if your in the theaves gulid one of the other members can get rid of your bounty.
To join the dark brotherhood, Kill somebody, then go to a hotel or what ever and go to sleep, Lucien will then come to you and ask you to join.
Here's a tip you can try KMAN, When you join the dark brotherhood and your asked to kill the first guy in a hotel as your "initiation test", (He's asleep in a Inn) lol you can walk over to the corner of the room go in sneek mode, then put something on your xbox controller so that your character is walking into the corner of the wall and stays there walking on the spot, Rufus or what ever his name is, won't wake up, and im pretty sure your sneak skill should go up. You can then just leave the game and come back in an hour and check up on your sneak skill lol.
And yes Sydzy you can get finger of the mountain spell from the book in the mage's gulid questline. But it costs a retarted amount of mana to cast.