OK, let's start off with a little background - there aren't too many of us out there who wouldn't like to lose fat AND gain muscle, right? Well, of course, but, the tough part is - how do you do it?
Q: How important is heavy training/lifting in getting these results?
A: Very important. Keep in mind that if you're not lifting hard you're not really giving your body a reason to keep the muscle you have, and certainly there's no reason for it to grow. The supplements can make a big difference - they will definitely enhance your results - but they don't create them alone. Of course, you also need to allow time for sleep so your body can recover and grow.
Q: How important is diet/nutrition in getting these results?
A: Probably even more important than the training. Of course, you need both heavy training and nutrition, but really, adequate protein and calories are the building blocks - if you're not on target there, then you're not going to see results - no matter what you take or how hard you lift. Just take a look around any gym - lots of guys lifting like crazy with nothing to show for it. But, with solid training, proper diet and the right supplements you can make serious progress - you really need all three - nutrition, training and supplements.
Here are some general nutrition guidelines - we suggest you shoot for a gram to a gram and a half of protein per pound of bodyweight each day and keep that up regardless of if you're working to lean out or bulk up. For overall calories, when you're trying to gain, go with 18-20 calories per pound of bodyweight each day, and when you're trying to lean up, go with around 12. Everyone is different, but these guidelines will help as a starting point in finding out what works best for you.