While this scenario is possible, I'm not sure it is the best choice. RadGrid is a complex control and it is probably not a good idea to try to render a new RadGrid in a "type ahead" or "auto complete" type scenario. Even using highly-optimizd web services, the number of browser DOM operations that would be required in that scenario are probably going to severly impact performance.
Perhaps you can provide some more detail on what you're trying to do? If you're tyring to filter a RadGrid, it has great built-in filtering support. It even support type ahead integration with RadCombobox:
That is probably a better approach if you want a high-performance page with sorting, filtering, and type-ahead support.
Hope that helps. Let me know if I can provide more assistance.