What about mkaing a few modifications to the JavaScripts so they are compatible with more browsers?
Perform a check for document.getElementId for NS 6 and over or for document.layers for NS4 browsers. A simple variable to store the objects you want to change in and the problems are solved...
It should only be a day of work (I did it myself for another site a little while ago, so I know what I'm talking about ;))