我无法让PHP在Mac OS X 10.7上运行

I've been struggling to get PHP up and running on my Mac. I have followed all the instructions on the previous discussion on this topic (How do you get php working on Mac OS X?) and it's still not working. When trying to open a .php file it displays it as the source code and doesn't even seem to recognise it as a PHP file, but calls it TextWrangler document instead.

In my /etc/apache2/httpd.conf file I have done the following:

• taken off the # in front of the LoadModule php5_module libexec/apache2/libphp5.so
• changed User to my username
• changed the DirectoryIndex to DirectoryIndex index.php index.html index.htm
• changed DocumentRoot to /Users/myusername/Sites/
• changed Directory to <Directory "/Users/myusername/Sites/">
• restarted Apache numerous times
• switched web Sharing on and off
• changed php.ini.default to php.ini

Still not working. Can you help?