To setup domain mapping from WordPress 3.0, you may follow the article as below.
1. Log into your fresh installation of WordPress 3.0.
2. Add the line as below to your wp-config.php
3. You shall be able to found Network from your WordPress tool as image below.
4. Click on the Network link.
5. You shall be asked for set the sub-domains or sub-directories sites to your network, select the radio button of sub-domains.
6. Click on Install button.
7. WordPress 3.0 shall guide you 3 step where you shall create the blogs.dir folder according to the given path, coding to insert to your wp-config.php file and coding to insert to your .htaccess file.
8. Once you have done, relogin again.
9. Next, you shall log into your cPanel and create the wildcard subdomain as detail below.
cPanel -> domains -> Subdomains ->
* (asterisk) and select your domain name.
your WordPress path.
10. Go to the Super Admin panel and select on Sites, add the subdomain.
11. Then select on Edit from the subdomain.
12. Change the value of Domain, Siteurl, Home, and Fileupload Url to suit to your new domain.
13. Edit your wp-config.php file again and change the value as below.
From:(assume that you are using domain.com)
define( 'DOMAIN_CURRENT_SITE', 'domain.com' );
define( 'DOMAIN_CURRENT_SITE', ''. $_SERVER['HTTP_HOST'].'' );