We have some sample code you can use that will accomplish that goal: http://community.constantcontact.com/t5/Documentation/Code-Samples/ba-p/25019. Which kind of server-side scripting technology does your server use (e.g., PHP, ASP.NET, etc.)? You can definitely grab the content from a SQL Server database as well. Is your form already built? If it is, I would look at using one of the libraries. If it is not, then the signup-form generator or sample forms might be a better option.
Richard Maxwell Support Engineer, Constant Contact