Beagle with injured tail / back - please help

Hi All,
My beagle is usually a happy go lucky dog with his tail ALWAYS up. 2
weeks ago, he jumped off the bed (at least this is how I think he did
it) and hurt his back.

His tail is no longer wagging and it always droops. He can hold the
base of it up when he relieves himself but hates to go upstairs and
will now avoid it at all costs.

Here are some photos:
http://dl.dropbox.com/u/15945493/xray1.png
http://dl.dropbox.com/u/15945493/xray2.png
http://dl.dropbox.com/u/15945493/gustail.jpg

Can anyone help shed some info on why this might be happening? My vet
mentioned that there's some minor calcification between 2 vertebrae
but that shouldn't be causing the drooping tail.

He has had NO walks or rigorous physical activity. His hind legs tend
to shake a lot when he is standing on all fours.
Please send me an email if you can help with this.