getting itunes from external drive

i had a g3 with the external, which has the itunes. it has since died, and now i have g4. when i plug the drive into the comp, i can see all the files on the drive, but when i open itunes it is blank. i have been able to open the folders on at a time, from the external, and then they are on the itunes library, but i dont know if they are taking up space on the comps memory. thanks for any help