Lunges definitely do require balance. I remember when I first started doing lunges with FIRM videos, I was teeter-tottery on many of them. It helped me to use a yoga mat under my feet to avoid any slippage and to therefore take out one of the balance challenges.
You can practice them using some kind of dowel or even a body bar for support, holding it perpendicular to the floor. Don't use any weights in this "training" stage.
When you do go into using weights, you might find that holding dumbells by your side gives you more stability than using a barbell behind the neck.
Also, doing a static lunge (where you only have to find the correctly balanced position once) may work better than front lunges. Rear lunges are second most stable, at least from my experience.