Sweeping is one of the coolest, yet most difficult guitar technique there is. It requires hand coordination between your picking, and fretting hand. To sweep, you must not pick each individual string, for that will give you a choppy sound, and you will never pick up speed with that. you must use a fluid sweep motion (pretend your pick is a broom, and you are sweeping the strings..which is the floor). This takes time to do, but this is the easy part; you still have to know what to do with your fingers. Sweeping is a way to play each individual string to a chord (arpeggio) with a fluid motion (hence sweep). take a G chord for example (picture above), and move that position higher on the neck. Yet, this isn't enough. You still need to have the coordination between your picking and fretting hand to successfully sweep. It takes time, but if you practice it correctly, then you will do it. I'll bet you all my glue that you will do it eventually. Check out the sweep.