for MS Office 12 - along with 9,999 other people - and I have been testing the beta 1 version of new suite for a while now.
You can't obtain the beta at this stage unless invited by Microsoft, but undoubtedly there will eventually be a public beta for download.
In the meantime I regret to say that Microsoft make you sign a pretty tight non-disclosure agreement as a condition of your beta-testing status, and that means I'm not allowed to write about it. I doubt that they would clap me in irons if I told you that in my opinion Outlook 12 is a big improvement on Outlook 2003........so I will.
Bear in mind that this is the developer beta 1 - and it doesn't contain many of the features which will be in the next beta version.