[Zope] zip files corrupted with IE when opened, fine when downloaded

[robert rottermann]

Hi there,
we have a problem with an intranet that runs using plone 2.5.3

when users using IE want to open a zip file from the intranet by using
the "open" option from the download dialog they get winzip complaining
that the file is corrupted.
if they select "save" from the same dialog they can open the zip archive
without problem.

does anyone know a solution for this or give me an idea where to look
for one?

thanks
robert