http://www.verious.com/qa/parsing-html-page-with-html-agility-pack/
추가 reference
http://refactoringaspnet.blogspot.kr/2010/04/using-htmlagilitypack-to-get-and-post.html
http://refactoringaspnet.blogspot.kr/2010/04/using-htmlagilitypack-to-get-and-post_19.html