Check out the following article at TechThrob.com.
An excerp of the intro:
This week Canonical, the company behind Ubuntu Linux, announced a partnership with Parallels, maker of the Virtualization products Parallels Workstation and Parallels Desktop for Mac. Consequently, the Parallels Workstation virtualization software is now available to download and install in Ubuntu Linux, completely supported by Canonical, and done entirely through the Add/Remove programs interface. This makes four different virtualization programs — three of which are installable via the package repositories — that run on Ubuntu Linux. (See the Correction: in the Installing VirtualBox section for more information)
This article compares four virtualization products available for Ubuntu Linux: the free, open source x86 emulator Qemu; the closed-but-free versions of VirtualBox and VMware-Server, and the commercial Parallels Workstation.