Expression 3 download is not for the faint of heart. I downloaded the install file twice and got the same error message during install both times. "Data1.cab file is corrupted." The install file is 57 Mb so you better be on a broadband connection. Here is a link to the site.
http://www.microsoft.com/products/expression/
The lead in screens make it sound like you have to have a previous version of the software but it never asked me for a serial number. You do have to have a Microsoft Passport account and an active email address to complete the process.

Good Luck! Maybe I will try again later.
dafipp
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update: Success! The third time is the charm. I was finally able to download and install Expressions 3.