Microsoft Update versus Windows Update...
Windows Update is the classic update service that only offers updates for Windows. Microsoft Update extends this service to cover other Microsoft programmes including, but not limited to, Office, Exchange and SQL (disclaimer: if you use Office 2000, or if your copy of Office was installed in "per user" mode, you will need to continue using Office Update- more information at the URL below):
http://support.microsoft.com/Default.aspx?id=907380.
How do we tell if we are using Microsoft Update or Windows Update?
First, if you are using Microsoft Update there will be an extra entry in your Program Menu. The Microsoft Update menu option will only appear in the Program List if it is in use.
If you are using Microsoft Update, it should be noted that the Windows Update link will also take you to Microsoft Update. This behaviour sometimes causes confusion, with a user recently saying in an email discussion I took part in that that because she had clicked on the Windows Update link she expected to be taken to Windows Update, and did not realise she was actually at Microsoft Update - it was her confusion that prompted this article.
Second, we can look at the picture immediately above the Express and Custom scan buttons:
Microsoft Update graphic
Windows Update graphic
The difference is subtle. Perhaps MS should include some color cues or a different icon to cater to those who skim the content of a page.
Swapping between Microsoft Update and Windows Update
Swap from Windows Update to Microsoft Update
Click on the Microsoft Update link as displayed in this screenshot:

or... click on the option to right of screen:
Click on Start Now, then Continue. You may next be prompted to change your Automatic Update settings (not compulsory), then click on Check for Updates.
Swap from Microsoft Update to Windows Update
Click on the Change Settings menu item:

Scroll all the way down and put a tick in the box. Click Apply changes now. You'll be asked if you're sure, confirm your choice and then you're done. The Microsoft Update entry will be removed from the Program Menu.
