What is it?

WindowsSearchIndexer.exe is associated with the MSN search toolbar.

What does it do?

From MSN:

"MSN Search Toolbar with Windows Desktop Search includes three toolbars that will change the way you search your PC and the Web. You can search from: Internet Explorer, Windows Explorer, Outlook and Your desktop."

More info:

Read more about msn search toolbar at [url=http://toolbar.msn.com/]msn.com[/url]