The name currently escapes me, but the story goes along the lines of that the protagonist, a high school student, who is a werewolf, meets a new student by the name of Elise.
Somewhere down the lines, she meets a stranger, and ends up becoming a vampire. That stranger is also targeting other students, and it's up to the protagonist, and a friend knowledgeable about the supernatural to put a stop to him. Prior to Elise being turned, there was not active conflict between the vampires and werewolves.
The only other info I can muster up is the book is from the late 80's - early 90's from the cover art, although I read it in my high school in 2008.