A great explanation of the PAP test is provided here as well as a chart listing the frequency that you should have a PAP by age range. Test results are also gone over and all types of abnormal cells are discussed briefly but well. False test results are talked about and astonishingly 1 in 20 women will have a false negative result. A good read but not as in depth material as the first two best 3 links.

Good resource that covers vital topics about having a pap smear: Who should have one?; Preparing for your pap; How it's performed; What your results mean; and, What causes false-negative results...a must-read!