Vista - datagrid column update vb 2005

Hi,
Total beginner in VB . I have a datagrid developed through vb 2005. I want to
edit a column but

col1.readonly = false won't work.
Here is my code
-------------------------------------------------------------------
Dim tableStyle As New DataGridTableStyle()
tableStyle.MappingName = "product"

'Product Code
Dim col1 As New DataGridTextBoxColumn
col1.MappingName = "prod_code"
col1.HeaderText = "Code"
col1.Width = 25

tablestyle.GridColumnStyles.Add(col1)
-------------------------------------------------------------------
I want to be able to update this column.
Any help appreciated

Pat