Give two weeks notice- it's the standard in business etiquette, and the minimum that is really proper. A week will look bad, and come back to bite you. If you give two weeks notice, your employer may escort you out immediately anyway, for security purposes, or may say they only need you for a week- so take the benefit of having been professional. If you're only giving a week, it's not enough to hire for your position, whatever that is. Looks bad.