If you hover over the images, many of them will tell you where they come
from.

For example, the woman at
http://office.microsoft.com/en-us/downloads/FX101321101033.aspx?pid=CL100570421033
says "woman working on a laptop (c) royalty-free/corbis" so I'd imagine it
comes from a set of stock images from Corbis. (http://www.corbis.com will
take you to the Corbis site where you can purchase CDs of royalty-free
images.)

If you click the "clipart" tab to go to
http://office.microsoft.com/en-us/clipart/FX101321031033.aspx?pid=CL100570201033
you can search for the word Laptop and turn up many comparable images, even
if they're not that exact one. (I don't have the patience to search through
51 pages of results, or I might find that the exact image is available
also.)

I've seen images there from Hemera, Corbis, Getty, and others. You can
search Google for "Royalty-Free stock art" or "Royalty-Free Images" to find
a number of such vendors.

As for icons, if you hover over the icon in the "things to do" section at
http://office.microsoft.com/en-us/downloads/FX101321101033.aspx?pid=CL100570421033
it says "(c) Microsoft." You can find at least some of them here:
http://blogs.msdn.com/jensenh/archive/2006/09/15/755336.aspx Download the
Office 2007 Icons Gallery and use Excel 2007 to open it. But these are for
developers to use when they create buttons in Office 2007 add-ins, so I
don't know that this will really help you. You might check some of the pages
at
http://www.google.com/search?sourceid=navclient&aq=t&ie=UTF-8&rls=ATSA,ATSA:2006
-01,ATSA:en&q=microsoft+icons+library
for more ideas.