I would suggest to check the new example from the Futures release:
There we are using a WebService request to load particular content in the RadToolTip, based on the current hotspot. In this particular case we use the Northwind database to fetch the list of customer from a given country. The list is populated in a Repeater and when you click on a customer ID, a RadWindow will be opened that contains the orders sent by this customer presented in RadGrid.
the Telerik team