Are we talking about custom drawing in iGrid cells, or you need to use a custom edit control based on the UserControl class to edit cell contents?
The former thing is implemented with the help of such events as CustomDrawCellForeground, the latter one requires that you wrap your user control into an instance of the iGCellEditorBase class.
Both techniques are described in the help file and the PDF manual for the control, but feel free to tell us more about your task on this forum so we can suggest a suitable way here.