The purpose of this research study is to evaluate and compare the effects of experimental treatments aimed at improving insomnia and nightmares in men and women military veterans between the ages of 18 and 60 years old, and who have a condition called Posttraumatic Stress Disorder. Insomnia refers to difficulty falling or staying asleep, although enough time is allowed for sleeping. Insomnia is also associated with daytime consequences, such as lack of energy, irritability, and difficulty concentrating. Nightmares are bad dreams that may or may not awaken the sleeper, and that cause discomfort during the daytime.