Japanese, Hebrews and Greeks? Any sources? The wikipedia article cites other mostly doubtful alleged contacts (with the exception of the Greenland Norse): en.wikipedia.org/wiki/Pre-Columbian_trans-oceanic_contact
Can't help you there as I can't remember the source and I just can't find the motivation to go scouring in the internet right now. I do know the issues are controversial and not yet accepted by the scientific community though, I can remember that much. The only thing I can expand on beyond what I already posted is the evidence found regarding Japanese migration.
*There is a people in South American who either all look Asian or a substantial percentage of the populace looks Asian. (Can't remember their name, sorry.)
*Pottery examples from these people dating back to around 2000bc match those of Japan from the same period.
*Analysis of mummified remains (mummified by the dryness of the Atacama Desert--scientific luck-out there) revealed that they suffered from a blood disease which is unique to one of the Japanese islands.
These three points, at least for me, indicate pretty strongly that the Japanese migrated to South America in pre-Columbian times. Oh, and the reason for the migration is believed to have been a volcanic eruption that occurred in the same time-frame.