If you use the CE version of DNN and recompile it over your newer versions of Telerik you won't have any issues.  If you are using DNN PRO then you are forced to use the version DNN comes with.  However, you can get around that by activating DNN with the standard PRO DLL's and then copy in your custom builds of DNN Pro.  The problem is that the Licensing module for DNN PRO uses the Telerik Grid and since you don't have the code for that you can't recompile over the newer Telerik.  

If you're ok with using .Net 4.0, then you can set the assembly binding in the web.config to use your newer Telerik and you won't have to deal with any of the issues above.  Otherwise, if you want to use .Net 4.5+ you'll run into the same problems.

A better option is to not use the Telerik Server Controls.  Use their client controls instead. 

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Professional DNN Extensions, custom solutions and mobile apps since 2003.
www.OnyakTech.com

Hallo thanks to both for the answers. I took a look around at jquery stuff but Telerik stuff is (to say the least) easier to integrate since are native .NET controls and I already mangled a lot with the demo version last year... I don't know yet... anyway from what Chris says (I'm on DNN CE) it seem I have to recompile the whole DNN to use the Telerik dll in my modules?
Isn't there a way to have both versions in the BIN folder (maybe renaming) so to be able to use the Telerik Dev dlls in my modules and leave the Telerik free for DNN and its stuff?

(as I said is a .NET newbie question don't blame on me heheeh)