Consider this scenario, you have a desktop/laptop running XP/Windows 7 on 32-bit and you would like to have a taste of SharePoint 2010. You could install VMWare if you can afford it and Hyper V supports only 64 bit Windows 7/Windows Server 2008. So what choices do you have? Until recently, none. But wait no more, there’s a new kid in town; a free open source solution from Sun, now owned by Oracle, called VirtualBox. In late June the product was updated so it can support 64-bit guest operating system on 32bit host OS. Other changes include compatibility updates for Mac OS X server guests, improved SATA performance and better command line parsing of installer on Windows systems.
VirtualBox is a general-purpose full virtualizer for x86 hardware that can be installed inside Windows, Linux, Mac OS X and Solaris virtual machines. It works on major x86 platforms and supports a large number of guest operating systems. Also, VirtualBox fully supports the standard Remote Desktop Protocol (RDP), implements a virtual USB controller and supports passing through USB 1.1 and USB 2.0 devices to virtual machines and USB over RDP. VirtualBox is very light (a typical installation will only need about 30 MB of hard disk space) and easy to configure. It works well with Hyper V images and it also allows you to take snapshots of the VMs so you can roll-back in case of troubles.
Keep in mind that hardware virtualization needs to be enabled on your computer, so the CPU has to support virtualization.