dude.
i think ur requirement is while selecting a particular row in datagrid.u need the details of that row in a textbox.
One method is using javascript method there is no sever side coding.I amnot sure.its possible through this.
Another common method is adding edittempalatecolumn in the grid.U can add this in the aspx page of ur form.
inside daagrid.
And in the properties window of ur datagrid u can choose editedindexchanged event. and can do ur codes.