If you want to run one OS from inside of another OS (a guest in a host), then a virtual machine (VM) is the way to go. The great thing about VM’s is anything you do in the guest has no effect on the host so it is ideal for testing. While there are many choices available for any OS you use, one choice to consider is VirtualBox. Vi

VirtualBox is an open source virtual machine software package which works on all major OS’s. There are many features which make VirtualBox attractive, such as mouse pointer integration in Windows and Linux (this is huge) and portable configuration files. VirtualBox is owned by Sun Microsystems, so this is a pretty good sign future development is in the works.

Personally, I use Microsoft Virtual PC 2007 for my work use, but the feature set of VirtualBox really has me considering giving it a try.