One of my customers is in the TAP program for Windows Vista Service Service Pack 2.  They wanted to use SCCM/WSUS to deploy updates to the Vista SP2 Beta clients that they have in production.  This is how we got the Vista SP2 updates in WSUS and SCCM:

1. Open the WSUS server console and right click on Updates.

2. Select Import Updates.

3. IE will open the Microsoft Update Catalog at  http://catalog.update.microsoft.com/v7/site/Home.aspx?sku=wsus&version=3.1.6001.65.

4. Search on Vista Beta

5. You should get something like:

6. Only the last two apply to Vista SP2 Beta.

7. Click on Add on each on them and then click on:

8. Click on Import.

9. Wait for the updates to get imported to WSUS.

10. Go to the SCCM Admin Console and force a WSUS sycn.  You should see something like this in the wsyncmgr.log:

11. The imported updates will now show up in SCCM and you will be able to deploy them.