If I understand correctly you want to use two different versions of Telerik assemblies in the same application. If this is the case, I can say that there is no simple way to do that. Our recommendation is to upgrade all parts of your application to use our latest release - Q3 2012. Of course we will be glad to help you with this task. Do not hesitate to contact us if you have questions, or if you need assistance.
If you still want to go with the two versions approach, I think the following thread
will help. It discusses a similar scenario.
Fell free to contact us if you have other questions.
the Telerik team