Einar,

Is it asp.net datagrid?
I had to dig for some code:)

Here is how you set the width:
Me.dgSearch.Columns(0).HeaderStyle.Width = Unit.Percentage(20)
Me.dgSearch.Columns(1).HeaderStyle.Width = Unit.Percentage(20)
Me.dgSearch.Columns(2).HeaderStyle.Width = Unit.Percentage(30)
Me.dgSearch.Columns(3).HeaderStyle.Width = Unit.Percentage(25)
Me.dgSearch.Columns(4).HeaderStyle.Width = Unit.Percentage(5)

Look at headerstyle property.