If you developing List Schemas drop what your doing and go and install this.
It is an expanded wss.xsd file containing a lot of descriptions and possible default values. When coding in Visual Studio using this will alter the schema defs and give you uber intellisense on your schema files.
If you already use wss.xsd in Visual Studio you will need to remove your reference.
Now if you forgot how you did that then the usual way I found of configuring it was to goto
C:Program FilesMicrosoft Visual Studio 8XmlSchemas
(or equivalent for your platform)
An to create a file called wsscatalog.xml, you may have called it something else but it contains xml like this
So go and remove that before installing this version as it won’t remove it for you and Studio can fight over things if you don’t or just not work at all as was my case.