>Also, what do you mean "your textbox class in defined columns." ?
If your base grid in the library already contains some columns, and you replaced default textboxes in them with your own textboxes, grid dropped on the form will inherit from your textboxes no matter were they mapped or not. But having columns in your base grid is not always convenient, because you cannot remove them from grid instance (if necessary)- they belong to the parent class.
I do not use this drag and drop feature for creating grids at all, and define all columns and controls in the grid by myself.

HTH

Nick