In king county washington, the county posts information regarding recycling centers in the area. One of the resources they list are the local salvage yards. As a remodeler, I find it is much less expensive, and sometimes even profitable to dispose of old doors, windows, carpet and the like at these places than to have them hauled off for scrap and pay the disposal fees.
Check with your local solid waste division.
Another way to find them is to check with some local demolition contractors. Look in the yellow pages. They ought to be able to point you in the right direction...
Have fun, and I agree with the caution. You don't want to install unsafe discarded items.