Virtualbox is a free Virtualization software for running Operating Systems within Windows or other host operating systems like Linux, Ubuntu, etc. You can download virtualbox at virtualbox.org Ubuntu is a free linux distro you can download from Ubuntu.com . You need a 800 MHz CPU and 512 MB or more of RAM/Memory  for XP, and I recommend 1-2GB for Windows Vista or 7 and 10GB of free space on your Hard drive.
The benefits of virtualization is you can use it to test software which you are not sure is safe or not or contain viruses since viruses in a virtual machine can not infect your main Operating System which is running VB in theory, but you should still practice good computer security practices like not visiting piracy sites, and adult entertainment sites since some of those types of sites contain malware, and viruses. Ubuntu has fewer viruses or virtually none, but it is best to play it safe and not visit harmful sites. Virtual Box Virtualization software  sandboxes its guest OS, so it can’t touch the main OS. But, there can always be a chance some hacker, or advance virus be able to hack into your main OS. Stay Alert, Stay Safe!
Be sure to backup your Virtual Hard drive by copying your virtual drive file to an external drive since the virtual drive and OS install can take up to an hour or more to finish. If you accidental wreck your Virtual OS by testing software, you can just delete it, and use your backup copy of your virtual hard drive which you can just remount.
Read my tutorial on Mounting a VMware VMDK file in Sun VirtualBox tutorial .
The disadvantages of virtualization is it can be very slow on older computers, and the animation and resolution can be difficult to set compared to a regular PC.
If your internet is to slow to view my video,  read my Tutorial for seting up a new virtual drive for Sun Virtual Box
If you want to learn how to install Flash Player to watch my videos on youtube, readInstall Adobe Macromedia Flash Plugin for Firefox on Ubuntu 8.04+ and above with .deb install file for Flash it is virtually the same installing Flash Player for Ubuntu 9.10 vs 8.04.
Also, you should read Update Ubuntu 9.04 which will also teach you how to update 9.10 for improve performance and bug fixes.
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