There was already some information available on the SQL Search syntax of SharePoint Portal Server Search.
Some of this documentation was for the old version of SPS2001, but did still apply:
Now there is some new documentation available: Microsoft SharePointPSSearch SQL Syntax (Preview). Have a look at: http://www.microsoft.com/downloads/details.aspx?familyid=d6a10783-a4e4-4463-8444-f88be48760b3&displaylang=en
This download includes a preview of the reference documentation for Microsoft SharePointPSSearch the SQL Syntax used for Microsoft SharePointPSSearch Full Text Search with Microsoft Office SharePoint® Portal Server 2003. Look for updates to this documentation in the Microsoft SharePoint Products and Technologies 2003 Software Development Kit (SDK).