How do they do that??
 

I was on www.trails-online.com, watching the quicktime files hoping to learn something, and I always see then balancing up on the back wheel without movement. How do I do this? Are there any balancing techniques?

What you are refering to is called a lurch or a real wheel bounce.

Its a fairly basic technique but is the fundamental skill to get anywhere in trials.

what they are actaully doin is when they they have there bike up on the rear wheel they are at the ideal angle (ie balancing point with the brake on)
They then let the bike fall slitely forward ( but then counter act that with around a quarter kick of the pedals to bring it back to the balancing point).
It is possible to do this on the spot with a little help from the wrists and upper arms which adds the small hop.
After practice this allowes for lurching forward or turing all, on the rear wheel.

Finding your balancing point on the bike is probably the hardest part of learning to lurch and then the combination of controlling the rear brake and pedal kick to retain your postion on the rear wheel. But once mastered this leads on to everything in trials

As you are using a FS bike if you were to try anything like that its best to lock up both your shocks as much as possible or idealy use a hardtail.

This is extremely breif and probably wont make any sence but there should be a better description on bike-trials.com

I am using a FS bike, but my back shock is pretty dang hard, so it's like a dampened hardtail. I can't wheelie yet, should I know how to wheelie before I try doing lurches?

Its probably helpful in a sense that you will learn about your balancing point and fethering the brake.

The only diff is that when you want to learn to lurch your balancing point will be different as you will be standing up on your pedals rather than sitting on ya seat.

But yeah try and master a mono first.