1. Download the Sharepoint AJAX Toolkit here - http://www.codeplex.com/sharepointajax
2. Develop a web part (VS project) to implement Bing.com Suggest type functionality using AJAX, .NET 3.0 and SharePoint Web services (you probably need the real code here huh! Email me if you need more information :)
3. Use the AutoComplete Extender in the Toolkit above by copying all the code out of the AutoComplete folder and paste into your web part project (as created in Step 2).
4. Compile and through errors and warnings find and add missing references, add more code files from the Toolkit as needed. Many common files were needed. Note that you need to set any .JS files to EmbeddedResources.
5. Use the MOSS 2007 Search API to build a ASP.NET Web Service to return a list of results based on input string value (keyword). Note that you need to host this web service within the same website (same port) as the Sharepoint site itself. Also dont forget to grant CAS trust for the Web Service assembly.
6) Post a comment if you successfully created the Bing.com type ahead search in MOSS, using the above steps