Bob Vila site article about residential sprinklers.

http://www.bobvila.com/HowTo_Library/Residential_Sprinkler_Systems-Safety-A2653.html

Key excerpts.
Stand-Alone vs. Multi-Use Sprinkler Systems
There are two main types of residential sprinkler systems: stand-alone and multi-use. Although both systems rely on the home's water supply, a stand-alone system utilizes its own piping, and may need a back-flow device. Stand-alone systems will use flexible plastic or copper tubing.
The cost of a home-sprinkler system will depend on a number of factors. A new-home, stand-alone installation can run anywhere from $1.00-1.25 per square foot,
insurance companies can offer discounts to homes with fire-suppression systems.