IPoint point = new PointClass();   
point.PutCoords(x,y);
IEnvelope pEnvelope= this.m_hookHelper.ActiveView.Extent;
pEnvelope.CenterAt(point);
this.m_hookHelper.ActiveView.Extent = pEnvelope.Envelope;
this.m_hookHelper.ActiveView.ScreenDisplay.UpdateWindow();
this.m_hookHelper.ActiveView.Refresh();