Thanks to VirtualBox

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).
Presently, VirtualBox runs on Windows, Linux, Macintosh and OpenSolaris 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, and OpenBSD.
VirtualBox is being actively developed with frequent releases and has an ever growing list of features, supported guest operating systems and platforms it runs on.

A screenshot of VirtualBox

Using VirtualBox it is very easy to switch between Operating Systems without restarting your PC.VirtuaBox comes with a simple user interface,so that even non computer experts can have a try on it.For those who are afraid to install a OS in their system by partitioning ,this is a very useful tool for them,so they can blindly trust that nothing will happen to their system if something during installation went wrong.We can install any no: of operating systems in your machine without worrying about the partioning scheme.You can also learn how to partition a system with this tool.So those who didn’t try VirtualBox till now,just try it out and see the magic.You will definitely say thanks to Sun Microsystems for developing such a great tool…. 
Those who want to try installing using virtual box,may use this link http://www.freesoftwaremagazine.com/articles/using_virtualbox_to_run_ubuntu