Ultrasonic Sensor Help

I'm fairly new to the arduino platform so I'm not to sure about how these work.
What is the purpose of the servo moving the sensor around and can you do without it?
and how far away can this sense objects?

Your help is appriciated!

What is the purpose of the servo moving the sensor around and can you do without it?

Measuring distances in different directions and yes, you can leave that out if you only want the distance in one direction.

and how far away can this sense objects?

Depends on the model you get and how well the object reflects ultrasonic waves. The PING))) from Parallax is rated for three meters: http://www.parallax.com/tabid/768/productid/92/default.aspx

Hey,
Thanks for your help! Soon I hope to have my sensor in the mail and attach it to the robot!