[Zope] Preloading images in Zope?

Hi, We are having a little bit of a problem with preloading images in Zope. On our display pages, we are preloading them in the usual way using Javascript, but we are finding that we are still getting a server hit when they are mouse-overed. This is only happening with pages (and images) in Zope. Has anyone come across this before? Know how we might be able to get around it? Thanks! Di