Itunes doesn't allow you to do custom sorting options,
It forces specific file formats on you
Its features for Music Playback are limited.
Syncing with Multiple devices is a pain, not everyone wants a ipod
as for using an western Digital External HD, does it fit the form factor that is in a notebook? is it SATA? way too many questions before that can be answered,
Provide the unit number on the HDD and I'll be able to tell ya, but chances are NO it will not fit.