Do you want to run multiple operation systems and easily run your operation systems from different computers?

The most popular way to do is this is by virtualization and and VirtualBox offers this for free.

This means that you can run Linux Ubuntu inside the virtualization software at the same time while running Windows 7 as your main OS  and  that you can easily copy your VM to another computer and run it from there.

The installation is straight forward and easy and VirtualBox is supported by all major operation systems.

About

VirtualBox is a powerful x86 and AMD64/Intel64 virtualization product for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL) version 2.

VirtualBox for Windows. Within VirtualBox Ubuntu 10.10 is running.

Presently, VirtualBox runs on Windows, Linux, Macintosh, and Solaris hosts and supports a large number of guest operating systems including but not limited to Windows (NT 4.0, 2000, XP, Server 2003, Vista, Windows 7), DOS/Windows 3.x, Linux (2.4 and 2.6), Solaris and OpenSolaris, OS/2, and OpenBSD.

http://www.virtualbox.org/

See also how to use a RAM disk to speed up your VirtualBox: Speed up your Windows applications with Dataram RAMDisk for Free [Best Performance - Freeware up to 4GB]

Test/comparison – VirtualBox vs. VMware Player 3.0

VMware Player is the alternative free virtualization software from VMware.
http://www.vmware.com/products/player/

VirtualBox has been tested against VMware Player 3.0 and showed to have a slightly higher performance. Other keyfactors for choosing VirtualBox over VMware is that VMware offers no support for Mac Users and has been known to have a faster update rate. Especially when it comes to compatibility with newer operation systems.

VirtualBox also provides a very rich platform to start/stop/suspend VMs, and manipulate the VMs in many different ways. If you’re using VirtualBox, it is extremely easy to write basic scripts that suspend all running VMs, connect drives, share files etc. without requiring any downloads or programming

Download – Installation

Here you will find the downloads for the various versions of VirtualBox:

http://www.virtualbox.org/wiki/Downloads

The installation is around 64 mb, but before you install an operating system as a guest, you should take into consideration that the host (your main computer) has adequate memory, CPU power and hard drive space. The installation is easy and simple and you are guided all the way by the VirtualBox Setup wizard. If you would like further information here is a link to the manual:

http://dlc.sun.com.edgesuite.net/virtualbox/4.1.0/UserManual.pdf

Share files and folders between host and guest OS
Go to Settings > Shared Folders and add the folders you would like to share. If you get have the error: invalid settings detected. It might be because Remote Display Server is turned on. To disable: Go to Settings > Display > Remote Display > uncheck Enable Server. When you have added your drives you use the following commands to enable the share in the Guest OS depending on which OS you are using.

 
Windows-Map Network Drive:

 
Linux-Terminal Commands:

Developer

VirtualBox also offers pre-built developer Virtual Machines, so if you want to cut the time installing OS and developer tools you can grab one the pre-built machines here:

http://www.oracle.com/technetwork/community/developer-vm/index.html

Administration

VirtualBox also offers phpVirtualBox.

An open source, AJAX implementation of the VirtualBox user interface written in PHP. As a modern web interface, that allows you to access and control remote VirtualBox instances.

http://code.google.com/p/phpvirtualbox/