I think you'll want to write a Custom Importer.
At this time, you can't replicate the functionality of the Title panel by a third-party plug-in. The Premiere Pro SDK doesn't currently expose a way to create custom panels. And you won't be able to trigger immediate updates to the Project Monitor when the user updates a title in your editor and hasn't yet saved it.
If you create a custom importer as bbb mentions above, you can provide a modal dialog for your title editor.
ImporterProcessServer is used in CS4, but no longer in CS5.x. In CS4, imGetPrefs8, which is the selector sent to tell your custom importer to display it's modal dialog, will always be sent from the main Adobe Premiere Pro process, and not from ImporterProcessServer.
Thanks a lot.