From Microsoft Security Response Center's blog:
http://blogs.technet.com/msrc/archive/2007/03/13/march-2007-bulletin-release-day.aspx

"So you have them, here’s the other upcoming dates for the regularly scheduled April 2007 bulletin release. The advanced notification is scheduled for Thursday, April 5, 2007. The April bulletin release is scheduled for Tuesday, April 10, 2007.

I did also want to confirm that with today’s release date, our support for the legacy WSUSSCAN.CAB has now expired. We will no longer be making updates to the old WSUSSCAN.CAB file. This means if you’re using MBSA for off-line scanning or are using SMS ITMU, you should be using the latest versions of these tools prior to the April bulletin release: information about any bulletins released in April won’t be included in the legacy WSUSSCAN.CAB, so you’ll need the updated tools to be able to detect and deploy any security updates released in April.