i take it that is the same for the users to clients as a user may have multiple clients? so create a column in clients table users_clientid and have a foreign key from userid in users table to this in the clients table?
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.