Bundlebits is a directory of ready to tun, turk-key operating systems and applications which have been authored with everything needed in one bundle of software. Simply download the software, either cut it to CDROM to install or copy to your VM host and create your new Virtual machine.

Virtualization allows one computer to act as a host, essentially allowing you to run multiple computers on one physical machine. The host allows it's resources to be shared across multiple environments.
These environments are known as Virtual servers and can consist of multiple operating systems, multiple applications, either locally or in remote locations. Operating systems include Linux, Windows (tm), and others. The obvious benefits are that of saving energy savings and lowering capital costs by more efficiently using hardware resources.
Added benefits include high availability, better desktop management, increased security, improved disaster recovery and simple management of multiple operating systems from one console.

There are a great number of resources on the Internet which can better explain how you can benefit from Virtualization techniques to maximize your hardware and resources.