Once you have upgraded to Leopard, any sites you have running locally won’t work, the problem is essentially that the config files have moved from /private/etc/httpd to /private/etc/apache2, BUT CARRY ON READING. You can’t just plonk your old config file into the new directory.

Here is what you need to do to set up the apache web server to serve your local site (and handle server side includes). You may need admin/root privileges for some/all of this, I can’t really remember and my notes are quite frankly illegible.
In the “/private/etc/apache2/other” directory create a file called “mywebsite.conf” and add the following text to it:

<Directory /Users/*/Sites>
AllowOverride FileInfo AuthConfig Limit
Options Includes
DirectoryIndex index.html index.cgi
<Limit GET POST OPTIONS PROPFIND>
Order allow,deny
Allow from all
</Limit>
<LimitExcept GET POST OPTIONS PROPFIND>
Order deny,allow
Deny from all
</LimitExcept>
</Directory>

AddType text/html .shtml
AddHandler server-parsed .shtml

Then in the ”/private/etc/apache2/users” directory create a file called “yourusername.conf” and add the following text to it (in the following example jojo is my username which you will need to replace):

<Directory "/Users/jojo/Sites/">
Options Indexes MultiViews
AllowOverride None
Order allow,deny
Allow from all
</Directory>

You will need to repeat this last step for each user that you would like to be able to host a site. When you have done this, restart websharing (under System Preferences -> Sharing) and then place your website in your “Sites” directory. You should now be able to browse to them in Safari (or whatever browser you use).