Same problem for me - I also tried all above suggestions (re. conf files and paths). As jewhanso says, I (also) get the message: Safari can’t open the page "http://localhost/..." because it could not connect to the server "localhost".
Leopard seems to lack a way of designating the local loopback address. Maybe this is IP v.6-related?
Does anybody know how to properly specify the local loopback address in IP V.6? Maybe that will work. I tried using both
http://localhost/~mydir/index.php and
http://127.0.0.1/~mydir/index.php. They work fine on my Tiger-based MacBook but not under Leopard.
Interestingly - in Leopard, the Apple > System Preferences > Sharing checkbox reads "Web Sharing" (using an external network address). In Tiger this is "PERSONAL Web Sharing" (using the local loopback address). The editing text-boxes disallow the use of 'localhost' or '127.0.0.1'.
There's an interesting error message in the apache2/error_log that reads "[Sat Feb 16 20:05:00 2008] [error] [client ::1] File does not exist: /Users/<mydir>/Sites/sites. Note the '... [client::1] ...' syntax. I don't know for sure but I am guessing this is an IP v.6 syntax - replacing the older syntax for the loopback address. I.e. localhost = IP address 127.0.0.1".
Looks like an Apple "faux pas" to me. :-/