Found the site info for this doujinshi and I recognized it from it's anime adaptation. Anyway, the full title for the game is (in romaji) "Otome wa onee-san ni koishiteru" and the anime's title is "Otome wa Boku ni koishiteru".

http://www.animecharactersdatabase.com/publisher.php?id=514
http://www.animecharactersdatabase.com/publisher.php?id=130

Update applied. Thanks.

[ Edited Dec 16, 2007 ]

私は日本語を少し読むと書くをできます。あなたも？