Currently I use a network drive to store music, photos etc so everyone in my family can access them from one location. Can I use OneCare to automatically back this drive up to either another network drive or a USB drive?
No, OneCare cannot back up date *from* a network drive.
I suggest looking at SyncToy for this - http://www.microsoft.com/downloads/details.aspx?FamilyID=e0fc1154-c975-4814-9649-cce41af06eb7&DisplayLang=en - it's free and you can create a task in Windows Task Scheduler to execute a copy operation on a schedule.
-steve