VMWare Workstation works with Windows 2000/XP/2003 as well as many flavors of Linux:
http://www.vmware.com/support/ws5/doc/intro_hostreq_ws.html#wp1000805

If you'd like to play around with memory access, in a similar fashion to a virtual machine, you may want to have a look at Bochs, a Free Open Source emulator, which can be found here:
http://bochs.sourceforge.net/

Looking at its source code might help you find what you're looking for