[Zope] Zope blocking client side image caching??, slow site loading

I am building a zope version of a asp website, done by another division in our company. Unfortunately it is much slower than the ASP one. The asp based site loads slow for the first page, but al subsequent pages are loaded fast due to the browser caching the navigation images. In the zope version the images seem to be reloaded for every new page request. Is there any way to change this and speed up loading of the Zope served pages. For comparison the asp site is http://www.unitekequipment.com the zope site is at http://209.48.159.60:8080/uml/ Regards, Frank