I know that it is a few months late, but I'm on the 64 bit Alpha 1 of Jaunty Jackalope (Ubuntu 9.04), and I found a solution to the problem. I haven't tried yet to get prism working, but I followed the instructions here and I have the server portion (the important part) working. Once you have performed the change described there, just go to your Zimbra Desktop directory and do Then you just need to go to http://localhost:7633/zimbra/desktop/login.jsp with your browser and it should work.
Update: Got prism working. That was the easiest part of the whole deal. I just did a
and then changed my desktop shortcut to use the version of prism that I just installed (change everything in the first set of "quotes" (ending in prism") to "prism" (without the quotes) and you should be all set.
sudo aptitude install prism
Update: OK, just kidding about the prism part. It's harder than I thought. I think I could figure it out, but I don't want to waste all day on it. The first part still works...