VMWare have just released a free (beer) version of their player (http://www.vmware.com/products/player/).
I wonder if you have considered making a VMWare image of the Zimbra system available for download. This would allow people to get a trial system up and running with very little hassle. Even Windows users could try it ;)
we're currently discussing that - the big downside of that is that the images are pretty hefty, so we're looking at ways to reduce the size before we go this route.
Yes the size of the download is a bit of a problem.
Have you considered distributing it as a BitTorrent?
If we go this route, that's what we'll probably do.