Taking music from other itunes

Hello,
I have an ipod classic and bought my parents one for christmas. My dad has a huge music selection and put all of his cd's onto his itunes. I tried to hook my ipod up to his itunes and drag albums over to my ipod but it would not let me. Then, I tried to do it with individual songs and they all had an exclamation point by them and they would not drag either. I have taken songs from other peoples itunes with no problems... What do I do?