To transfer your music to an external drive see this knowledgebase article from Apple. For iPhoto, see this article. This is doable but the downsides are (1) you can only use iTunes or iPhoto when you are connected to your external drive. If you forget and launch the program without the drive connected you'll see nothing. Even worse, if you aren't careful (2) you might forget and download photos or music while the external drive isn't connected and then you have a mess.