Hello Jill-Connie Lorentsen,
If I understand your requirement, you are after the AutoComplete functionality of our DropDownList. If this is the case, you can employ this feature in RadGridView by setting the AutoCompleteMode property of the GridViewComboBoxColumn, for example:
categoriesColumn.AutoCompleteMode = AutoCompleteMode.Suggest;
I hope this helps.
All the best,
the Telerik team
Q2’11 SP1 of RadControls for WinForms is available for download (see what's new); also available is the Q3'11 Roadmap for Telerik Windows Forms controls.