The version of Visio that comes with VS Enterprise Architect has a forward-engineer feature that will generate SQL. There is also a type library for the modelling engine, but (on older versions at least) it won't extract certain items such as comments. However, the generated SQL has the comments in a fairly simple structure that does facilitate parsing the generated SQL.

1. Powerdesigner Alternative
2. Download Powerdesigner Viewer

You can get older versions of VS enterprise architect on E-bay for not very much money (I think mine cost about £250). One caveat for reverse-engineers is that all pre-VS2005 visio DB modelling engines will not play nicely with the SQL Server 2005 native client.

Powerdesigner Alternative

You need to either script out the database and re-load it on a SQL2000 server (dealing with SQL2005 specific features such as schemas is left as an exercise for the reader) or get a more recent version.

Download Powerdesigner Viewer

POWERDESIGNER IS AN ARCHITECTURAL AND DESIGN TOOL THAT CAN VISUALIZE AND MANAGE THE IMPACT OF CHANGES TO YOUR SYSTEM BEFORE IT HAPPENS, SO THAT YOU CAN RESPOND TO CHANGES CONFIDENTLY. POWERDESIGNER IS A PROFESSIONAL MODELING AND METADATA MANAGEMENT TOOL THAT CAN BE USED TO DESIGN AND CONTROL METADATA DATABASES. POWERDESIGNER IS VERY EASY TO USE IN DATABASE MANAGEMENT, DISPLAY DATA IS JUST TABLES AND GRAPHS, SO THIS DOES NOT CONFUSE PEOPLE WHO DO NOT KNOW THE DIFFERENT QUERIES FOR THE SQL DATABASE.