The MBR (Master Boot Record) is just a space on your disk where the bootloader is held. All pc's have MBRs (that I know of) just as most OS's have their own boot loader, it just happens that Linux uses Grub and/or lilo. From my experience with the Windows bootloader it only loads Windows whereas lilo and Grub will load pretty much any OS you would care to put on your computer (correct me if I am wrong someone). It's not a stupid question at all. We all have to start somewhere.