Here's some small info i got from the JumpUSA newsletter:

SQUATS
Squats are the best exercise an athlete can do for strength if it is performed correctly. If not, it can be the most dangerous exercise. When working with young athletes, I see that 9 out of 10 squat incorrectly. This will lead to injuries, not improved athletic performance. The two main problems are: an excessive forward lean of the upper body (which can cause low back injuries) and excessive forward movement of the knees (which can lead to knee problems).

The key points of a good squat are:

• athletic stance
• the bar across the upper back (on traps and shoulders, not the neck)
• the chest out and the back tight with a slight forward lean
• the knees stay directly above the feet at all times
• sit back deep to parallel, keeping weight on the heels

Before attempting squats, have a trained professional analyze your technique to make sure it is fundamentally sound. Concentrate on technique, not how much weight you can lift.