Nicotine, like all stimulants, does increase your metabolism slightly, but not really enough that you could lose a lot of weight just from using it.  
  
From my research and experience, generally speaking, any form of cardio is going to burn more calories at a time than weight-lifting. A 30 minute run is going to burn more than a 30 minute walk, but aerobic exercise burns more calories faster. If you're a powerlifter and you deadlift 600 pounds as your normal workout then that might change but that's an extreme example. 
  
The thing about lifting weights though is that as you build muscle, it takes more energy to maintain that muscle mass, so your body will have a higher resting metabolism. If you're losing fat that's a good thing, but if you're trying to build and maintain muscle then you'll have to eat more.  
  
In the end, it's good to do a little of both, but intense cardio gives you more bang for your buck. If you ever go on /fit/ don't fall for the "cardio kills gains" meme, only noobs and hungry skeletons believe that nonsense, it's more complicated than that.