Check out these crazy (in a good way) underclockers from Germany here. I've done some crazy experiments in the past like this, but not to that extreme. A lot of people wonder why someone would want to do something like this, but I understand why they do it - because they can.
You can learn a lot of tips and tricks by doing experiments like that.
They could have done the XP install on a faster system, installing the Standard PC HAL, delete as many devices as possible from the Device Manager, SysPrep the drive and then move it to the slower system. On first boot it would detect all the hardware so as to skip the slower setup process. I'd love to see a system benchmarked at 4.77MHz. It'd be like an IBM Pentium PCjr.