Banner rotation issues

Hi,
I'm completely new to JavaScript and am probably asking a question that has been around for years. Please be patient with me.

I want to rotate my CL, ShareSale, and LinkShare, (even Adsense???) banner ads within the SideBar of my pages. I found some Simple Banner Rotation code at spyka.net/scripts/javascript/simple-banner-rotator that basically does what I would like, with one huge exception.

This particular banner rotation script as well as others that I have found all force me to hard-code my banners into my pages in some form or another. Lots of pages equals lots of work.

What I am hoping to do is place all of my banner code into a separate file (would that be a .js file?) and then just grab new banner code from that file, according to a specified size, as the rotation function runs. That way I only have to update the one file to change my available banners.

I also need to be able to limit the number of banners that are displayed in my SideBar based on the length of my Content DIV since my pages all vary in length.

I doubt I am the first person to ever what to do this so I suspect there is code available for these tasks. I simply have no idea how to find such code.

Please help! Thanks very much!

Sterve