Boot Xbox Media Center on (almost ) any PC from a USB flash disk
Theoretically, you should be able to boot XBMC on any PC no matter what operating system you're running. In practice, you'll need a PC that can boot from a flash disk and a supported graphics card (or some Linux hacking skills). NVIDIA drivers should be supported out of the box, but ATI and other graphics cards, not so much. The LiveUSB is based on Ubuntu Hardy Heron, so if you're up to the challenge, you might be able to add support on your own.
Creating the bootable media using Windows takes just a few moments. Just download the LiveXBMC image and builder files, unzip them to the same directory, insert a 1GB or larger USB flash drive (which will be reformatted), and click the LiveUSBBuilder.exe file to get started. A few moments later you should have a bootable version of XBMC. Or a flash drive that will start to load the media center suite and then crap out about halfway through the process. But definitely one or the other.