Apple made a excellent move today and announced the beta for a new Boot Camp utility. This lets you run Windows natively on the new Intel Macs without needing to come up with special hacks to trick old school OSes that need BIOS instead of EFI (and also includes all necessary Windows drivers in one place).
Another really handy thing is the utility it comes with to create/resize partitions without loosing any data from the existing ones (no format needed).
Apple is a hardware company primarily, so they still get to sell the hardware… and in the course of doing so, plenty of people will switch to OS X because it might be their first (incidental) exposure to it (if they bought the machine to run Windows).
Windows running on a Mac is like Windows running on a PC. That means it’ll be subject to the same attacks that plague the Windows world.