This one is simple.
copy it across. intact.
it just works.
a few things to do before you copy it across though – consolodate it so that all the music is in the itunes folder. you might want to let itunes sort all the songs into folders – just goto itunes prefs and advanced then hit ‘keep itunes folder organised’
once you have it all in the right place just copy it all across – its up to you how to do that – you could make a network share for that folder – if you are in windows then unenable simple sharing, then right click the itunes folder and click share on network.
you could copy it all onto dvd’s or even cd’s but thats a waste of environment, not to mention time and effort. you could do what I did and get a usb / sata adaptor and rip the drive out of your machine and plug it in as an external usb drive, or you could transfer it to a real external drive then transfer it again onto your mac.
once you have the music on your mac, in your ~/Music/iTunes directory just open up itunes and it should find your library, and will just work after a couple of minutes.