The matter is off topic here, but...
VMWare: Software that permits you emulate an environment to run another operating system or application of another operating system. VMWare has version for Windows and Unix/Linux.
For example: There is appliances that run under VMWare in windows that run Fedora 4 core minimal installation, Fedora 5, Debian with KDE, puppy linux, etc. You start an instance of VMWare and "boot" your appliance inside of the VM created by this instance.
My question is about the opposite, e.g., start an instance of VMWare in linux and boot windows XP inside this instance.
If you sear for VMWare in Google you'll find lots of pages. In popular P2P there are lots of programs and appliances related.
You can begin with:
http://www.vmware.com/