When I export some data to excel, and open it with excel 2003, every number cell has a green triangle in the top left corner and has the error "Number stored as text".  How do I specify that the cell contains a number?

The way I'm adding data to the excel file is:

Workbook workbook = new Workbook();
workbook.Worksheets.Clear();
Worksheet sheet = workbook.Worksheets.Add("Test");
sheet.Rows[0].Cells[0].Value = "String"
sheet.Rows[0].Cells[1].Value = 0.0;
BIFF8Writer.WriteWorkbookToFile(workbook, filename);

Thanks.

-Nick