Security Assist is a tool to ensure that users have the correct credentials to "log in" or "access" a certain page or set of pages (or an entire folder). It allows you to create rules based on the session variables and database information about a user depending on what you set up for user authentication upon log in.
What you are probably looking for is Validation Toolkit where you can validate the content entered by the user. WebAssist's CSS Form Builder gives you the ability to build forms, add CAPTCHA (to test that the user in human) as well as other techniques. CSS Form Builder includes Server and Client validation, so I would check that out.