Your .htaccess and wp-config.php seem to be correct as well as your wildcard dns entry.
It looks like the problem is with your apache vhost. You have to include the wildcard entry in your vhost for Multisite to work correctly.
<VirtualHost *:80>
ServerAdmin [email protected]
ServerName mysite.com
ServerAlias www.mysite.com
ServerAlias *.mysite.com
UseCanonicalName On
DocumentRoot /home/mysite/public_html
ErrorLog /home/mysite/logs/error.log
CustomLog /home/mysite/logs/access.log combined
</VirtualHost>
If you want to use domain mapping you will need to add a vhost entry for each domain mapped site.
Also make sure you have NameVirtualHost set up in your ports.conf file
NameVirtualHost *:80
Listen 80