What makes a person invest tens of millions of dollars in dozens of fine violins, violas and cellos? "Looking back at it, frankly, it's a kind of madness that seizes you," violin collector David Fulton told me in an interview last month. "When I bought my first good violin, I thought that was going to be it. And in fact it was, for 10 years or so. But always had the idea in the back of my mind, 'Gee, wouldn't it be nice to have a Strad, if I was able to do that...'" A co-founder of Fox Software who eventually served as Microsoft’s Vice President for Database Products unt...