I have been having the same problem
Yesterday I typed in http://localhost/xampp/index.php
and it worked fine and create my tables. Today I typed it in and it can up with.......
The requested URL /xampp/index.php was not found on this server.
When I type in just http://localhost/
I get a page saying that Apache is working from the Apache webserver.
i'm using mac leopard if that makes any difference.