you can run the computer either as a mac or as a pc, from an operating system point of view. you can't run the mac and pc programs simultaneously, but the project and sound files are the same. so, let's say you use cubase, reason and ableton. the disk for any of these progams contains both mac and pc versions, so you just install them with each OS. now you like your mac for ease of use so you whip everything together on the mac, then you save the files on a keydrive or whatever, switch to windows and load them into cubase so you can use those free vsts!

it's a little bit of a pain, but worth it to get the versatility of a pc for music but have the clear superiority of osx for most computing purposes...surfing the web is the most obvious...imagine a world where you never need to run an antivirus program, never need to remove spyware from your computer, etc.