Windows Vista New User?

So i want to sell my computer i have my own account and mainly every website ive went on ive had my pword saved if i have an acount with them. i dont want the next owner of the computer top access all this and im not sure how to restore my whole system since its vista and all ive had was a xp..i created a new user account and it looks like everythings from scratch but im not 100% confident that they wont be able to access all my other info that was on this pc..does it work ..do you kow for sure? or does any one know how to get the whole computer running like new again?