See the blog posting at http://blogs.technet.com/mu/archive/2007/08/14/the-microsoft-update-catalog-v1-is-live.aspx for more details. For those of you who have been looking for one place to download content from Microsoft Update and Windows Update, this is the place. Content available includes security updates, drivers, and much more. For all the items you want to download, place them in the download cart and download them in one big batch.
For security updates, the web site will download the needed MSU file that you can import into BDD 2007 Workbench. For drivers, it will download a CAB file containing the needed driver files, so you'll first need to extract the contents of the CAB file before you can import them into Workbench.
I do have to say, though that some of the files names that it uses are quite entertaining. Here's what it called the driver CAB file that I downloaded: