DataTable woes

For some reason I am unable to update a DataTable.

I've got a foreach(DataRow row in dataTable.Rows)

but if I assign row[whatever]=something;
and go row.AcceptChanges();

the changes don't get applied.
I think I may have to create a row object and do an Update. That's my initial hunch.
It worked in code above the foreach, but it was a little different there.