Try this:
var listOfUsers = (from x in context.CMSPI_CODICIACCESSO
join u in context.CMSPI_ANAGRAFICAINFOBASE on x.IDANAGRAFICA equals u.IDANAGRAFICA
select new {
RowA = x, RowB = u
});
DataTable result = new DataTable();
foreach (var x in listOfUsers)
{
result.Rows.Add(x.RowA , x.RowB);
}
--Amit