Here is a great video on using your Weber as a smoker
I have been using my gas grill with good results. It is a 3 burner grill and I heat is up to high and then turn off the center grill. I put the meat in the middle and my wet chips in a smoke box on one side (you can use a pie pan covered in foil and poke holes in it). I, then, turn the grill down to low on the side burners and let my meat smoke for several hours. This is a great way to do ribs.