"SANTA CLARA, CA February 12, 2008 Sun Microsystems, Inc. (NASDAQ: JAVA) today announced that it has entered into a stock purchase agreement to acquire innotek, the provider of the leading edge, open source virtualization software called VirtualBox." 
This is the first time I heard about VirtualBox. Immediately I went VirtualBox website and download VirtualBox binaries on Windows, VirtualBox_1.5.4_Win_x86.msi. It's quite small, only 17Mb. It takes less than one minute to install.
There are a number of options for various virtual images: complete Windows family, Linux, BSD family, OS/2 and Solaris. I created a Linux 2.6 virtual disk and installed ubuntu 7.10 iso.
However, the screen resolution of guest system is surprisingly low, 800x600 and 640x480. After I did some search on VirtualBox forum , I finally can get the "real" full screen. I summarize the solution here:
1. Finish guest OS installation and start the guest OS.
2. There is an ISO file in VirtualBox installation directory, called "VBoxGuestAdditions.iso"
In Windows, by default, it is located at C:\\Program Files\\innotek VirtualBox\\VBoxGuestAdditions.iso
Click "Device"-> "Install Guest Additions" to mount this iso file.
3. Find "VBoxLinuxAdditions.run" as shown below. Run it in a terminal window, "sudo /media/cdrom/VBoxLinuxAdditions.run"
4. Run "sudo dpkg-reconfigure -phigh xserver-xorg". Select "vboxvideo" as video card and all of screen resolutions you want
5. Edit /etc/X11/xorg.conf as super user
6. Restart X by press "Ctrl+Alt+Backspace".
1. VirtualBox is easy to use. I did not find that I have to consult any user document in order to start using it.
2. VirtualBox's functionality is equivalent to VMWare Workstation. I can create various virtual images on my own. More importantly, it is free. VMWare Workstation for Windows would cost US$189.00.