About:
Dehydration techniques have come a long way in recent years. Old technology left as much as 30% moisture in the dehydrated products. Nor did these poorly dehydrated foods store very well. With present technology, moisture levels have been reduced to 2% or 3%. Gone are the pliable dehydrated foods. Now they break with a crisp "snap" when bent. With moisture levels reduced to 2%-3%, storage life has been increased to several years.

How:
Dehydrating is best when using a dehydrator because it is more energy efficient. If you must use an oven, be prepared that your home will be heated and your energy bill might be a bit higher than usual.
How to Dehydrate Vegetables at eHow.com
Dehydrating Food at BackPackingChef.com
How to Dehydrate at NESCO®
Dehydrating preparation, time, uses

The review of the Sedona SD-9000 says,
"For raw foods enthusiasts, this is especially important because it means that when you set the Sedona dehydrator at the recommended temperature of 118°F, you can be sure the temperature will not exceed this setting, thus protecting the activity of enzymes that are harmed at higher temperatures."

Dehydrators: (a sampling)

Brand	cost	trays	tray size	watts	adjustable temp	timer	comments
Nesco FD-37 & FD-39, FD-35 Snackmaster	$39	4-5	13½ diam	400	n	n
Nesco Snackmaster FD-60 & 61	$65	4-12	13½ diam	500	y	n
Nesco Snackmaster FD-80	$80	4-8	14" x 14"	700	y	n
Nesco Gardenmaster Digital Pro FD-1040	$140	4-20	15.5" diameter	1000	y	y
Excalibur 3526T	$250	5	15" x15"	400	y	y
Sedona SD-9000	$370	9	15" x 13"	600	y	y	computer controlled

Source: Choosing a Food Dehydrator at BackpackingChef.com
See also Food Dehydrator Comparison Table at Dehydrator Review

Homemade Dehydrators:
You can make your own dehydrator

You can even use your car as a dehydrator.
See Your car as food dehydrator | MNN - Mother Nature Network
and Use Your Car as a Food Dehydrator at lifehacker.com

Links:
How to Dehydrate Vegetables at eHow.com
All About Dehydrated Vegetables at USAEmergencySupply.com
Dehydrating Food - Fruit, Vegetables, and Meat at provident-living-today.com
Dehydrator Review at DehydratorReview.net