Engadget is reporting that Windows doesn't have the necessary fan drivers to run the fans on the Intel Macs, with a risk of overheating:
According to a thread on MacRumors, the current XP install doesn't include a fan driver, which means your Mac's fan never goes on. That may not be a big issue if you're using an iMac for limited periods in a well-ventilated space, but if you're planning on running XP on a MacBookPro, you may find things getting mighty hot. We're not dissing narf and blanka here; they won the contest and deserve their $13,000. But you may want to be a little careful before trying out their solution at home.
I can imagine this causing a few fried CPUs until someone makes a driver, which fortunately probably won't take very long. This sort of bug serves to bring those of us excited at the prospect of running Windows on our Macs back down to earth with the realisation that, even if it is possible to install Windows, it might prove very difficult to actually run it. I hope that someone sorts out all the potential bugs promptly, 'cos I would so love a Mac that can run Windows too!