Well, sort of. Target date is 2006 or 2007. But at least we now know for sure the next major release of Exchange Server, codename "E12", will run on 64-bit Windows and will be 64-bit enabled. What does it mean? Stay tuned.
http://hellomate.typepad.com/exchange/news/
http://www.windowsitpro.com/Article/ArticleID/45129/45129.html
http://www.eweek.com/article2/0,1759,1752710,00.asp