Answer to: How to switch it on without the power button?I haven't had many Mac's open but on most standard Motherboards there are jumpers you can jump together in order to start the machine. To find them you'll have to disassemble it and follow the start button's wiring itself. This may not work for your Mac however but on most Window's based desktops and laptops this works.
Answer to: Can I use a pc hard drive for boot campJust a correction to your post Majesty, It is possible to boot into an external drive/Flash drive from Windows. You need to ensure the BIOS allows you to boot from the device. If a computer won't allow it you may need to consider flashing your BIOS if possible. I have a flashdrive that can run many verisions of Linux and Windows if I choose.