Try searching for ~* in the directory that you want to search.

The Tilde (~) lets you use the old DOS search syntax. The asterisk (*) means "return everything".

You could also use type:NOT"file folder" which would exclude the listing of all the folders but show all files.

Some sources for advanced query syntax:

http://msdn.microsoft.com/en-us/library/bb266512%28v=vs.85%29.aspx

http://msdn.microsoft.com/en-us/library/aa965711%28v=vs.85%29.aspx

http://www.microsoft.com/windows/products/winfamily/desktopsearch/technicalresources/advquery.mspx