Does anyone know of some good tools to extract sqlserver schema information, including the stored procedure definitions, and output them in a form suitable for comparison (XML perhaps ). It needs to be able to run in ant or have an api to write to and extra points if it can do the diffing between extracts.

Schema extraction and comparisons
Boris Jabes MSFT
Hello,
You may want to see Kentico Compare SQL - http://www.comparesql.com. It compares database table schemas, procedures, views and functions. It's now available for only $49!
Frank0824
Don't re-invent the wheel and use 3rd party utility to compare the structure and the data of your SQL Server databases, like ApexSQL, Red-Gate ... tool.
You can also use this free tool :
http://www.sqldbtools.com/Tools.aspx