Thanks guys... i wasn't looking for a rotating header or randomizing it.
Just want to replace it every week or two. I realized that many guys were still seeing the "old" header since they don't log out.
So just changing the graphic name is probably the quickest and easiest way - using the CP.
By the way, I do use a "changing graphic" in one of my islands -- "Wha Sup?" It changes every day to a new graphic and text. I have set it up with 365 days. (although I only have about 100 graphics so far)... but it's cool and it keeps the site "fresh".
http://vcca.org/forum/--Bill