Getting Windows to run on a G4 (effectively) is quite a trick, as it's a completely different processor, so would have to run entirely in emulation, making it painfully slow on a G4.
God knows how you get Windows Mobile on an iPhone -- again, completely different processors.
The iPad is on Apple's A-series of chips, which is a system on a chip, but based on an ARM Cortex A8, which Windows ARM version is supposed to run on. So, it's technically possible, if not easy.
But iPads are really just big iPhones, so if he did get Windows to work on an iPhone, I can't see him being stumped by an iPad, given that he is pretty amazing to have achieved what you claim.
Can I ask: what is it particularly that you "need" Windows for on an iPad, and might there not be an alternative way of achieving your higher goal?