I have downloaded/purchased an audio book to my ipod & it is in German. Is it possible to convert it to English?

You can't convert it yourself. What does the audiobook's description page in the store say. does it say that it's in English in German ? You can try the 'report a problem' page to contact iTunes Support : http://reportaproblem.apple.com

If the 'report a problem' link doesn't work then you can try contacting iTunes support via this page : http://www.apple.com/support/itunes/contact/- click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption