QEMU - Wikipedia, the free encyclopedia:

"QEMU is free software written by Fabrice Bellard that implements a fast processor emulator, allowing a user to run one operating system within another one. It is similar to projects such as Bochs, VMware Workstation and PearPC, but has several features these lack, including increased speed on x86, and support for multiple architectures in-progress. By using dynamic translation it achieves a reasonable speed while being easy to port on new host CPUs."

Speed should be comparable, maybe a bit slower than VMware - but it's free!

- and you can even get a (linux) system to boot from an USB-stick:

QEMU-Puppy - A Personal Portable Computer
http://www.erikveen.dds.nl/qemupuppy/index.html

- and, it even seems you can use QEMU for creating a shell for VMware Player (?)

Creating an XP Pro VM for the free VMware Player
http://johnbokma.com/mexit/2005/10/26/vmware-player-windows-xp.html

(the hack comes from here:
How-to: VMware player modification
http://www.hackaday.com/entry/1234000153064739/
This shows how to create an empty VMware shell, that you then can install using the free VMware Player
)