How to add a picture of a head to a person in a videos body

[Richie]

hey guys,
i was wondering how can i add a picture of someones head to a video so like if i was walking in a vid i could get a pic of someone elses head and stick it to my head in a video if you get what i mean :S

[The Professor]

Using Ulead's program (which isn't owned by them anymore and I forget the name, search around :P) there's a timeline for an image overlay, just stick an image on there. Idk how to do it with other programs though