From Times Online:

Modern humans and Neanderthals had sex across the species barrier, according to a leading geneticist who is overseeing a project to compare their genomes.

Professor Svante Paabo, director of genetics at the renowned Max Planck Institute for Evolutionary Anthropology in Leipzig, will shortly publish his analysis of the entire Neanderthal genome, using DNA retrieved from fossils. He aims to compare it with the genomes of modern humans and chimpanzees to work out the ancestry of all three species.

Modern humans arrived in Europe from Africa about 40,000 years ago to find Neanderthals already living there. The two species then co-existed for 10,000-12,000 years before Neanderthals died out ?