If you're attempting to make something to swing like spider-man, not to crush your hopes, but it's impossible to do unless you have a body like spider-man. Other than that, even an Olympic athlete couldn't. Now, if you're trying to make something similar to batman's grappling hook, this is completely possible! The only problem is that its expensive and big. The military currently has the smallest motor winch system to pull you up, and it's about the size of a large lunch box. It's also very heavy and uses a lot of power, so there is still a lot of work being done on it. There is also another version on the market, but its even more heavy and needs to be plugged in to a wall to work. You also have to connect it to your waist for fastest use, or you can do something similar to the way batman and robin used to climb in his old TV show with Adam West, but I don't think you want that. If your connected it straight to your arm, while it is also very heavy, to have all of that weight on your arm would rip it off, or the winch would slip off and go without you, causing you to fall to your death. To make your weight shoot out in the way you want it too, a motor will not work. Baseball cannons wouldn't have the required power, and those things (minus the hopper) are pretty big. Luckily, scientists and the good people of the internet have already solved this problem years ago! CO2 is definitely the best way, and it's not very expensive. However, if that's not the way you want it, the next best thing is spring loaded. This wouldn't be as powerful, and your would have to be pretty strong to reload it.
The way I see it, the best possible grappling hook your could make would be a gun, spring or CO2 powered, that would shoot out your hook, which is connected to your rope. Once you fire and let it hit something, your put your feet on the wall with your hands on the rope, and start walking up the side of the building. This is slow but its the most practical way.
For a look at experimental firearm power on the subject, check out what BYU did on it:
http://www.youtube.com/watch?v=YwFTYtMfJ7U
Well, that's my own scientific approach to you're situation. I hope I helped! Feel free to ask any questions!