Did you know that WordPress 3.0 includes a new multisite option? This option is very useful in case you run many WordPress websites on sub domain or even with their own separate domains on one WordPress installation!
Make your current installation of WordPress manage multiple WordPress sites, the benefit is that you only have to manage and maintain one installation of WordPress, a big time saver for web entrepreneurs that own and operate multiple WordPress sites.
The official tutorial on how to set WordPress network of sites.
Currently WP Multisite works only on sub domains or folders, to map individual sites to independent domain names use WordPress MU Domain Mapping plugin.