I have to add:
Martin's answers show that something happened for that entire time (from that time to the present). ex "The tribe has hunted here for a thousand years."
You can also say something happened at that time. ex "The tribe hunted here a thousand years ago." Instead of hunting for those thousand years, the tribe only hunted there a thousand years ago -- it is not continuous.
Since one thousand years ago can be used as cause and effect (e.g. Since the tribe hunted a thousand years ago, we found arrow heads where they hunted.) or as a continuous action, like Martin said (e.g. The tribe has hunted here since a thousand years ago.)