Hi George,
The RichText cell control in the library allows you to edit richtext via a dropdown panel. It does not allow you to edit the text in-place.
You can derive the GridRichTextBoxCellModel and GridRichTextBoxCellRenderer classes to use an embedded RichTextBox in the cell to do the active editing.
See the following forum for more details.
http://www.syncfusion.com/support/forums/grid-windows/32438/Rich-TextRegards,
Jisha