Postherpetic neuralgia is a distressing syndrome of neuropathic pain that continues for at least 3 months after the resolution of the varicella-zoster rash (shingles), can last up to years later, and for which therapies are often limited by incomplete pain relief and side effects. This is a randomized (study medication is assigned by chance), double-blind (neither the Investigator or the patient know the name of the assigned study medication), placebo-controlled, crossover, parallel-group, multicenter study to determine the effectiveness and safety of 200 mg of RWJ-333369 given twice daily for 4 weeks compared with placebo in patients with Postherpetic Neuralgia (PHN). The study hypothesis is that 200 mg of RWJ-333369 given twice daily for 4 weeks will be more effective than placebo in reducing pain due to PHN, as measured by average daily PHN pain scores. Patients will receive 200 mg of RWJ-333369 or matching placebo tablets, given in equally divided doses twice daily by mouth, with or without food, for 4 weeks in each of the 2 treatment periods.