Interesting article in today's New York Times outlining evidence that the Americas might have been settled by the Solutrean people of Iberia, sometime around 20,000 BC. A number of stone points and other tools have been found on the east coast, both on land and some miles out to sea, that have been indirectly but consistently dated to that time period, which is considerably earlier than most evidence for a migration via Siberia. A much larger Arctic ice cap and lower sea levels might have allowed a "coastal" voyage (i.e., along the edge of the ice cap) from Europe to North America, and the lower sea levels would explain the tools dredged up by fishing boats some miles offshore: they would have been on dry land when deposited.
And so, there is speculation that the Solutrean people might have had skin-on-frame boats, and that they migrated east-to-west, living a kind of pre-Inuit maritime hunting culture and not stopping until they reached the relatively benign climate of the Chesapeake Bay.
Even if this speculation is correct, it doesn't imply that the Solutreans then went on the populate the Americas. A small East Coast colony might have remained for some time and then died out, leaving the Americas again unpopulated until about 15,000 BC, when the Siberian migration took place.