Quit iPhoto, ensure your Backups ares done.
iPhoto, Drag and drop the iPhoto Library in Pictures to the External, Rename the one on the internal, so you can identify it.
Click on iPhoto with Option Down, choose the Library on the External.
Confirm the Copy was good.
Remove the one from the Internal.
Quit iTunes
iTunes, drag the iTunes Library from Music to the External Drive.
In iTunes Preference > Advanced > Change Media Folder.
Quit and Relaunch iTunes ensure your Files are all there.
Remove the Library from the Internal Drive.
Don't forget to do a backup before you start.