VirtualBox is a virtualization application that can help you run any x86 and AMD64/Intel64 compatible operating system on host machine. VirtualBox runs on Windows, Linux, Macintosh, and Solaris hosts and supports a lot of guest operating systems such as (not limited to) Windows NT 4.0, 2000, XP, Server 2003, Vista, Windows 7, DOS/Windows 3.x, Linux (2.4 and 2.6), Solaris and OpenSolaris, OS/2, and OpenBSD. VirtualBox 4.1.4 is now available for Ubuntu 11.10 Oneiric Ocelot.

Adding VirtualBox repository:
  • sudo add-apt-repository "deb oneiric contrib"
  • wget -q -O- | sudo apt-key add -
  • sudo apt-get update
Installing VirtualBox 4.1:
  • sudo apt-get install virtualbox-4.1
If you want USB 2.0, VirtualBox RDP and PXE boot for Intel cards support on your guest machines, you have to install extension pack that can be downloaded here.

Installing extension pack
Once extension pack downloaded, open VirtualBox and navigate to "File -> Preferences", at the "Extensions" section, click icon "Add package" and locate your downloaded extension pack.

And then follow on-screen instructions.