Hi Jane,
I guess one of the questions would be, how far ahead you were thinking of booking.
When we walked in April 2009, we booked well ahead for SJPP @ L'Esprit du Chemin and also for the albergue @ Orrison. Beyond that it is probably a bit restrictive to book to far ahead.
Like others have said it is not neccessary to book ahead, but you can, if you feel like you would be more comfortable doing so. Take a mobile phone, a list of accommodation, write out a few phrases of Spannish, "do you have a bed for tonight (or tomorrow night), how much, thank you, my name is". I think you will find most people will be very helpfull and are used to people not being fluent in spannish. Another option is to ask someone, were you stay one night, if they would ring ahead for you, and book for the next night. But as has been mentioned this will have to be in private albergues, hostels, hotels etc.
Buen Camino
Col