In reply to Domgalea:
We climb in the Harz and the Ith fairly regularly, but I've never seen any English guidebooks, although if I remember correctly, the original "Klettern im Norden" has an English intro and access details. As has been said previously, the guides are pretty much in topo format, so you can generally find your way to the main areas ok. Where in Germany are you based?
JW