I'm almost sure you got the error above directly in your console when you try to start the server. This is in fact a warning which should not prevent your server from running. I just tried to recreate the same situation:
[root@home conf]# /etc/init.d/httpd start
Starting httpd: [Wed Jun 14 15:34:07 2006] [warn] The Alias directive in /etc/httpd/conf/httpd.conf at line 546 will probably never match because it overlaps an earlier AliasMatch.
[ OK ]
[root@home conf]# /etc/init.d/httpd status
httpd (pid 5622 5621 5620 5619 5618 5617 5616 5615 5614 5612) is running...
To see the "real" error that prevents your webserver to start, you should have a look at your apache error log (probably something like /etc/httpd/logs/error_log... check your ErrorLog directive in httpd.conf).