Hi... Ok, I think I can help everyone with how to move your iTunes Music Library, both the iTunes library.itl file as well as your whole actual library of your data (mps, mp4, songs, movies, home videos, podcast, etc)... to a new computer or new HDD or something like that.
first thing you need to do is completely turn of iTunes and don't let it be open.
then tunr off your wifi or internet connection.
then you need to do is find where you have your actual library of your data (as noted above is). if you are novice mac user its probably in your Music folder which is in your user name... something like Macintosh HD/Users/Your User Name/Music.
if you are a little more advanced... it might already be in a different location like a HDD or such like mine was.
it is gonna be called either iTunes Music or iTunes Media depending on how long ago you started using iTunes... Mine is iTunes Music as its been a long long time for me.
so after you find it, move this database of all your files (noted above) to where you want to move them to.
then hold down the option key and open iTunes. it will ask you if you want to create a library or open library. you can do either one but i just created a new one to start from scratch. you can call it what ever you want.
***NOTE on above, this is where it gets confusing. It is not actually creating a new database of all your files, it is creating an iTunes library.itl file that is the Apple way of knowing your library. this is where it gets confusing.
so after you created new library or opened current library, iTunes will open.
Now go to the menu bar ITunes and select Preferences.... Then Advanced. You will see "iTunes Media folder location". Here you need to press the Change button to the right of it and then find where you copied your actual database library of all your songs, movies, and other media files to as noted above. select it and press Open.
you will see the "iTunes Media folder location" now changed to where your files are.
below it you will see some boxes....
Make sure that the "Keep iTunes Media folder organized" box has a check mark in it. but that "Copy files to iTunes Media folder when adding to library" Does Not have a check. This is important. If you have a check here, in later steps its gonna move your music again. we will come back to this box later. all the rest of the boxes below it don't matter and are based on your preferences although i would definitely Not Check the "Automatically delete watched movies and TV shows box" for sure.
now Ok out of there and nothing should happen yet. maybe a quick library update window that should go away right away but maybe not..
again, make sure your wifi or internet is still not connected.
now, here is the big one... go to the Menu bar "File" and then down to the "Library" then click the Right menu "Organize Library" and a Box will open up that states "Organize Library". there are two boxes. put a check mark in "Consolidate files" but No Check Mark in "Reorganize files in the folder "iTunes Media".
Pres OK and wait away. Depending on how much stuff you have this could take a long long time. Let it run run run.
when it is done, you should have all your files now in your iTunes .itl file and they should all show up. You might have to reorganize them a bit but should be all good to go.
after this is done, go back to the Preferences tab then to the "Advanced" tab and put a check mark in "Copy files to iTunes Media folder when adding to library" and press OK. this will allow for any of the actual files of any new items that you add: music, movies, etc to be put in the same location as all your other stuff.
After it is all done, you can now reconnect your internet and the iTunes will eventualy show any other items you have purchased online with like a cloud next to it so you can re-download it into your new library.
hope this works as it worked for me and took some time to figure out how to do it again.