LINQ To DataTable, Finding Duplicate Rows?

Using the following DataTable:

Dim d As New DataTable()
d.Columns.Add("Product", GetType(System.String))
d.Columns.Add("Value", GetType(System.Double))

[code]....

I'm trying to use LINQ to identify if there are more than one of any type of product. In SQL, this would work something like:

SELECT Product FROM SOME_TABLE HAVING COUNT(*) > 1

I can't for the life of me work out how to do this in LINQ. I was following someone who did something like this:

Dim q = From row In d.AsEnumerable()
Group row By New { column1 = row("Product"), column2 = row("Value") }
Into grp

[code]....

But I get an error when I try to actually use 'q'. how I can make this work?