Latest news is that Office 2010 (and Project, Visio and Sharepoint 2010) are on track to release to manufacturing next month. Unless something unexpected happens, they are supposed to be released to businesses on May 12, 2010. Regular users who don't have enterprise agreements will have to wait until June for the software.
I'd expect that they would be on MSDN at the May 12 date as well if history is any guide.
To keep sales from completely stalling while people wait for the next version, Microsoft has also announced a "tech guarantee" which will give you a free copy of the 2010 version if you buy a 2007 version after March 4, 2010. Details are here: http://office2010.microsoft.com/en-us/tech-guarantee/