Virtualization Alternatives

Virtualization is the method by which guest operating systems can run within another "host" operating system

Available Options for virtualization as my knowledge

• Sun VirtualBox
• Virtual Pc for Microsoft (I don't discuss here, people complaining about its performance lack and other integration issue on web) .
• VMWare Server (I don't discuss here,Its not user friendly ,lightweight as virtualbox)
  

I tried myself only sun Virtualbox with Ubuntu host and guest version windows vista and XP and host XP and guest Ubuntu .I find it really awesome ,even no one can feel that vista or XP running over Ubuntu (when its full screen mode) .It share all devices like network ,sound,usb serial port, display card what ever in your system.

Some VirtualBox features written on its website (which I tested myself) which are:

• Modularity. VirtualBox has an extremely modular design with well-defined internal programming interfaces and a client/server design. This makes it easy to control it from several interfaces at once: for example, you can start a virtual machine in a typical virtual machine GUI and then control that machine from the command line, or possibly remotely. VirtualBox also comes with a full Software Development Kit: even though it is Open Source Software, you don't have to hack the source to write a new interface for VirtualBox.
• Virtual machine descriptions in XML. The configuration settings of virtual machines are stored entirely in XML and are independent of the local machines. Virtual machine definitions can therefore easily be ported to other computers.
• Guest Additions for Windows and Linux. VirtualBox has special software that can be installed inside Windows and Linux virtual machines to improve performance and make integration much more seamless. Among the features provided by these Guest Additions are mouse pointer integration and arbitrary screen solutions (e.g. by resizing the guest window).
• Shared folders. Like many other virtualization solutions, for easy data exchange between hosts and guests, VirtualBox allows for declaring certain host directories as "shared folders", which can then be accessed from within virtual machines.
  
  A number of extra features are available with the full VirtualBox release only (see the "Editions" page for details):

• Virtual USB Controllers. VirtualBox implements a virtual USB controller and allows you to connect arbitrary USB devices to your virtual machines without having to install device specific drivers on the host.
• Remote Desktop Protocol. Unlike any other virtualization software, VirtualBox fully supports the standard Remote Desktop Protocol (RDP). A virtual machine can act as an RDP server, allowing you to "run" the virtual machine remotely on some thin client that merely displays the RDP data.
• USB over RDP. With this unique feature, a virtual machine that acts as an RDP server can still access arbitrary USB devices that are connected on the RDP client. This way, a powerful server machine can virtualize a lot of thin clients that merely need to display RDP data and have USB devices plugged in.

My recommendation If you need to work on multiple Os , don't think just install sun's virtualbox.












Vista Run Over Ubuntu Host
References
http://www.virtualbox.org/wiki/VirtualBox
http://www.brighthub.com/computing/windows-platform/articles/29183.aspx
http://www.mangoorange.com/2007/07/05/5-reasons-why-you-should-use-virtualbox-instead-of-virtualpc-or-vmware/