I really don't know. You may need to contact adobe about this. If you have a valid purchase of CS3 then I don't think your license would expire.
You could always purchase the current version and update your sites with it.
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.