localhost / 127.0.0.1 generates 404 Not Found

When I start the Apache server through System Preferences -> sharing and then point my browser to localhost or 127.0.0.1 I get a

"Not Found
The requested URL / was not found on this server.

Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.
Apache/1.3.33 Server at XXXXXXXXXXXXXXXXXXXXX Port 80"

Might I have misconfigured something? It feels like a root should always "be found"

Any help much apreciated!