Chris Lee interview from the Sunday Times.
This interview doesn’t tell you anything you don’t know, but if you follow the link to Norwegian daily Dagbladet, it shows Lee sitting in front of what looks like the concept art for Orthanc. (more)
On second thoughts, no spoilers. Several people wrote in to point out that the sketch is one of Tolkien’s own, and it’s over at Rolozo TolkienPosted in Old Main News on December 4, 2000 by Tehanu