How are you getting the value for the user id currently? By default the only user id that would be available to you in the admin is the id for the administrator user. To get the id for a regular site user you would need to use the session variable for their id or something like this. On the front end of the site the id is held in a session variable when a user logs in. So on any of those pages you can make reference to this users id whenever they are logged in.
Please post back and describe a little more about the specifics and what you are trying to accomplish and we will help you out with whatever we can.