I often run into the following problem.
I work on some changes to a project that require new tables or columns in the database. I make the database modifications and
Two book recommendations: "Refactoring Databases" by Ambler and Sadalage and "Agile Database Techniques" by Ambler.
Someone mentioned Rails Migrations. I think they work great, even outside of Rails applications. I used them on an ASP application with SQL Server which we were in the process of moving to Rails. You check the migration scripts themselves into the VCS. Here's a post by Pragmatic Dave Thomas on the subject.