larger image popup help

Where and what do I edit to have better control of the popup window for veiwing "larger" images?

(by "larger" images I mean, when you click on a product image to see the "larger" (usually!) version of the same image)

I'm using a clean install and custom template (based off the new "classic" template in version 1.3.5).

I want to manually set the size of the popup window (currently it's sizing itself fine in Firefox, but is dreadfull in IE).

I also want to manually set the background of the popup window (currently it's using my mainpage back-most image, wich is FAR too noisy to veiw a forground image directly over).

I've searched the forums but found a lot of conflicting how-to's and what-files, such as references to files I simply can't find. I'm assuming said files are from older versions of Zen Cart or different templates or... who knows!

Any help on this, or a pointer to an up-to-date how to on this would be MUCH appreciated!

-zami