How important and good are such calibaration DVDs?
Since it is impossible to properly calibrate your system without the correct tools; I'd say its extremely important. Such calibration DVD's really should come with every HTiB (and a test-CD with every cd-player).
Other tools you'll need:
*Tape measure (for speaker distance)
*SPL meter (to measure speaker/subwoofer settings)
Some people also use tripods to hold the SPL-meter in the same place for the entire speaker-level setup. But it isn't required. The Radio Shack
analog SPL meter is available at any Radio Shack, and is the cheapest SPL-meter you're likely to find ($39).
BTW: the Sound & Vision Home Theater Tune-Up DVD is also a good calibration DVD and costs less than half of what Avia does.