Derek's answer is right. This is the best way to go. For different condition, you should use DataTriggers in the style.
This is the way to go because the DataGridControl does Container Recycling which will reuse an instance of DataRow to display other business object. You don't want to explicitly set the value on DataRows or DataCells sinc they will be permanent and you'll get weird behavior in your grid.
Xceed Software Inc.