Here are several links to articles on Christianity and Harry Potter. I have not had time to read all of them, but the first of them is a great post on a recent interview with Rowling and what she says about her struggling faith.
http://www.dallasnews.com/sharedcontent/dws/dn/religion/stories/DN-weiss_28edi.ART.State.Edition1.2758dd6.html - a great article on the presence and absence of Christianity in HP
http://www.pres-outlook.com/tabid/1676/Article/5310/Default.aspx - this one is from a Presbyterian point of view
http://justindburton.wordpress.com/2007/07/26/a-really-really-ridiculously-insightful-dont-forget-long-harry-potter-post/ - discusses several HP themes