Aqui ficam alguns links para o site da msdn relativo aos schemas e sintaxes utilizados pelo web service de pesquisa (search.asmx)

Overview

http://msdn2.microsoft.com/en-us/library/ms543175.aspx

Query Schema

http://msdn2.microsoft.com/en-us/library/ms563775.aspx

Sintaxes (SQL, Keyword e URL)

http://msdn2.microsoft.com/en-us/library/ms561536.aspx