apple go to lengths to make it painful, and my experience of this is that they have gone to increasingly further lengths in increments over the last 5 years. you end up having to install some funky efi bootloader like refit or refind, even if you want to use bootcamp to install windows (i've never seen bootcamp work correctly on its own, although i have heard that it does work sometimes) - even then you end up having to hack things to get it to work correctly, or find that things like the trackpad or keyboard mysteriously don't work properly if at all...
mounting your hdd into a vm in os x is often a necessity.
its a nightmare. apple don't want you to do these things.