How can I get the number of rows in my DataGrid

One way you can do this is through the BindingManager.Count property.

[C#]
	int numRows = dataGridDetails.BindingContext[dataGridDetails.DataSource, dataGridDetails.DataMember].Count;

[VB.NET]
	Dim numRows as Integer = i dataGridDetails.BindingContext(dataGridDetails.DataSource, dataGridDetails.DataMember).Count;