Open iTunes and select File > Library > Organize Library > Consolidate Library.
Let it do it's thing.
Then move all the music and the iTunes music library into the Shared folder that you will find inside the Users folder on the hard drive.
Now the two accounts, yours and your girlfriends, will be able to access the same music library.
When you first launch iTunes, after the move, you will need to point iTunes at the relocated iTunes library.
Do this by holding down the Option Key and launching iTunes.
Click Choose and then navigate to the Shared folder and the iTunes Library.
This is the way you should have done it in the first place.
I probably made some unwanted changes to my Music folder. I use my MacBook together with my girlfriend so I created another "user" and wanted to share the music library with her. Therefore I opened the iTunes music foler in Finder (HD/my user name/Music/iTunes/iTunes Music), went for info, in "Sharing and Permisions" set the user name, alowed to read - but nothing hapend. So I added to "Aply for enclosed items". Since then the most of the items of my iTunes music folder are locked - they are there but I (the main user of the Music Folder - but not administrator) cannot access to the data unless I give permission - but I have to do it for each and every one of them separately, which is ... grrrr .. long and impossible with 30GB of music! and also Finder says that in Music folder is only 4BG as recognize those files with no access as "--" without a size. I think I did do something wroooong :-/
Is there any way how to unlock all the files? I tried give the permission for the whole music folder but then even those files which I have unlock are locked again.
Oh, just spoted another thing: when i go for info for each folder and look at the Sharing & Permissions/Users there are TWO administrator names, one user name of my girfriend but not my user name! So when I unlock it and add myself for permission to read and write one of the administrator's names replaces mine. So there is me, girfriend and ONE administrator. And the Library is on administrator's name - reloaded form backup to different user account. It's all mess, I know.
I hope someone will help me.
MacBook3,1 Mac OS X (10.5.8) iTunes 9.1