If you believe that the Neanderthals were a seperate species than the humans alive today (which I don't), then the last Neanderthal lived about 28k years ago. This is the belief of most anthropologist/archaeologists in the world today. They believe that modern humans first appeared about 150k years ago. There have been periods in human history that different species co-existed but, it was a long time ago. A good book on this subject is
Extinct Humans by Ian Tattersall, released a couple years ago.
The group that we call the American Indians today first appeared in North America about 6,000 years ago and are believed to have their origins in North China.
>This is the belief of most anthropologist/archaeologists in the world today.
I think you are behind the times on this one, blam. Go to any world-class conference on this subject and see most of the pioneering anthros distancing themselves from the old Darwinian theories and old texts and moving the dividing line up to ~10,000 years ago and closer. Some are still holding at the close of the last ice age, ~13,000 years at most.