Couldn't find this anywhere on t'interweb so after some fiddling, here's how to move an iTunes library from one user to another on the same computer on OSX (leopard in this case and iTunes 10.1)
Now this only works if you're using an external drive like me, or some directory outside the home directory of the user.
First, logged in as the new user, open iTunes and go to iTunes - Preferences - Advanced. Now change the 'iTunes Media Folder Location' to the directory of your old iTunes library (the directory in which you have 'music' and other directories. Save the changes and quit iTunes.
Now time to delve into terminal. For this you need to have access to root or any other user that can access both yours and the old user's home directory.
Now all you have to do is copy the ~/Music/iTunes directory of the old user to the same location of the new user. In my case:
cp -R /users/admin/Music/iTunes /users/musicserver/Music/
Check the permissions on the copied directory, should be owned and read/write by the new user, then quit terminal and reload iTunes. Now your old library should appear :o)
If not... see me after..