Who's afraid of difficult women? Not four Web-savvy independent bookstores in the San Francisco area. The four stores -- Booksmith, Printers Inc., Cody's and Capitola Book Cafe -- are collaborating on a Web ring to promote the in-store appearances (which begin May 5 at Booksmith) of Elizabeth Wurtzel for her new book, Bitch: In Praise of Difficult Women (Doubleday). Each Wurtzel site is linked, and they offer all kinds of information about (as well as photos of) the fetching Wurtzel; her writing, her problems -- you name it. After each appearance the stores will post Wurtzel's responses to audience Q&As.