Hi,

1)
Are you using templates?You can either go by Cells property or by FindControl(ctlid)for the datagrid item.
2)I am not sure if I remember this correctly but you can set the width/height of the columns ar runtime by using datagrid.columns[index].header/footer/item.style.width etc=Unit.Percent(10).
Intellisens will be of great help for this:)
Hope it helps,

VLad