$find is not from jquery, but comes with ajax. Though i am not sure from which library it comes from, i think it comes with the framework.
One thing you could check just to be sure, is if you have a scriptmanager on your page?
But i don't think radgrid would work at all without one.
3.Add a ScriptManager control on top of the page in which you are going to add any RadControl.
Good luck, perhaps you are on the right track now to find the problem :).