http://www.canadianparents.com/articles/feature91f.htm states:
Night terrors occur less commonly and are different from nightmares. Typically, children with terrors are out of control, but still awake. They may be sitting up in bed, appear frightened, staring with eyes wide open. They may also be sweating, breathing heavily and complaining of seeing peculiar things or objects that are not really there. This period of "terror" may last for up to several minutes and then the child will usually go back to sleep.What distinguishes night terrors (which occur in less than 5% of children) from nightmares is that the child does not recall the dream or event leading to the night terror, and in many cases, does not recall that anything at all happened during the night.

Here are some interesting sites on Night Terrors.

http://www.aafp.org/afp/20000401/2044ph.html

http://www.cincinnatichildrens.org/health/info/growth/diagnose/nightmares.htm

http://ga.essortment.com/nightterrorssl_rmge.htm

http://www.stanford.edu/~dement/terrors.html

http://www.bipolarchild.com/newsletters/0007.html

http://www.parasomnias.com/html/night-terrors.php3

http://health.family.org/questions/A0000570.html