I am considering buying a laptop and I'm interested in a MacBook but I will be mostly using Windows environment (Win 7 or Win 8). If I buy an Apple laptop, can I install Win 8 on it? If so, how?
According to this post, you can install Windows 8 with Bootcamp just like Windows 7. Windows 8 supports the same drivers as Windows 7, and as Bootcamp is basically an installation tool plus a bunch of drivers for mac hardware, there is no reason it shouldn't work.
If you are thinking of getting the Retina MacBook Pro: While Windows supports high-resolution displays (by increasing the pixel size of fonts and graphical elements), it's not perfect. Just like Mac applications that have not been made "Retina ready", many Windows applications will look blurry (or too small). That's likely to change when there are more high-dpi Windows laptops available, but for now it may be a problem. See also this blog post.
Also note that battery consumption might be worse using Windows if your MacBook as a dedicated graphics chip, as the bootcamp drivers don't support switching it off.
If you're mainly using Windows, and just occasionally want to use OS X, you could also try to install OS X on your Windows notebook. Apple doesn't allow it officially, but if that's not a problem for you (or the country you live in), you can give it a try. Here is a list of compatible hardware, you should also google around a bit. If you have the right hardware, it's not harder to install OS X than any other OS (or to install Windows on a Mac). I can't give you instructions here as people don't like the topic on this site, but search for the 'always up-to-date guide' for a good starting point.
I thought this would be worth adding for anyone else - Bootcamp now officially supports Windows 8.
So yes, you are able to install Windows 8 on your Mac laptop (so long as the support article linked above shows your computer in the compatibility list). I believe Bootcamp uses a wizard to run you through installing any Windows release to your Mac, but I may be wrong.