Quoting or using copyrighted material created by someone else in your own work can open up a can of legal worms that might turn into a lawsuit. Copyright law allows "fair use" of copyrighted material, but what falls under that doctrine isn't cut and dried. Reviewing or critiquing someone's work or quoting a small portion of another's creative material to illustrate a point usually passes muster under the fair use doctrine, but mere acknowledgment for other uses may not be sufficient. Rather than acknowledgement, you might have to obtain permission.
Fair use of someone else's copyrighted material generally applies to works used for educational or scholarly purposes, not for financial gain. The amount of material you use also figures into the concept of fair use. While a snippet is one thing, a substantial amount of the work is another. If your use of the material affects the value of the copyright in any way, it doesn't fall under the fair use doctrine. If a copyright owner believes you have infringed on his copyright, he can file a civil lawsuit against you for damages.
Contacting the Copyright Holder
In the best-case scenario, you can obtain permission from the copyright holder to use the material, even if that means paying a fee or royalty. The United States Copyright Office charges a fee for a copyright search for pre-1978 material, but you can visit the USCO in Washington, D.C. and search on your own for free. It's likely that you can search for copyrights registered after 1978 online.