I second everything Halfdan said, with a minor remark. With standard word order, as displayed in (1) and (4), the "stress", if any, is on the verb. If you want to stress that you, as opposed to everyone else, didn't see him, you simply have to stress that you, which is not necessarily standard, although Halfdan's examples might indicate this. Do note that this distinction cannot smoothly be made in writing.
A few examples, where (1) is standard and the other two simply variations, to further clarify:
(1) Jag såg honom inte. - No stress. Was he there? Well, you didn't see him.
(3) Jag såg honom inte. - Stress on jag. He might have been there, but you didn't see him.
(2) Jag såg inte honom. - Stress on honom. You didn't see him, but yes, you saw others.