I'm not sure about the permission denied error. I use Mamp for my local setup. As far as can anyone outside see your site if placed in the web root directory, it depends on your exact setup. A lot of people have routers and connect to that so their computers aren't directly connected to the net. In this case your site would only be accessible from outside if the router is setup to forward port 80 to that computer. If you don't have a router and Leopard is setup to accept connections on port 80 then yes someone outside could see your site, but only if they know your IP address.