I lift weights twice a week, one day lower body, one day upper body, and have followed this pattern on and off for years and always get great results with it. I don't enjoy abs work, and tend to stick it at the end of upper body, lay on the floor doing crunches at home, or go to a class that has some abs work in it. Years ago, I used to follow a more complicated workout routine - legs, back and biceps, legs, chest and triceps, legs etc - but was in top shape and training with a man well experienced in body building. These days, two days a week is all I need.
What the previous poster is saying is correct about needing time for your muscles to recuperate in between lifting weights. When you lift weights, you are putting small tears in the muscles and they need time to heal. That is why you need to increase your protein intake as well, to help the body heal.