Maighstir: Windows XP
Mode (which is effectively a preconficured VM with Windows XP preinstalled, running on VirtualPC) requires Windows 7 Professional, Enterprise, or Ultimate. However, if you have a Windows XP licence lying around, you're free to install that to a virtual machine (whether you're running Microsoft VirtualPC, VMWare Workstation, VMWare Player, Oracle VirtualBox, or qemu) regardless of your underlying OS.
RevolutionSphere: I still do a have XP Licence, which VM would you recommend?
* VirtualBox is simple enough, and has some Direct3D 9/OpenGL support.
* VMWare Workstation is the most powerful/function-rich by far, but does cost money and is likely more than you actally need.
* VMWare Player is a "lite" version of Workstation and - I think - has similar hardware capabilities as its brother (with 3D support and whatnot).
* I don't like VirtualPC at all (it has one good thing - all its emulated hardware identifies as "real" hardware that has drivers for any OS you may install).
* qemu is neither fast nor user-friendly (it's good on Linux, due to KVM for speed and libvirt for userfriendlyness, and it can emulate several CPU architectures because it actually emulates the CPU rather than passes it though).
There are other hypervisors (Hyper-V for Windows 8 and Server 2008 and newer, Xen for Linux, Solaris and NetBSD, ...), but I don't know much about those.