You can use LINQ and still keep the results in an ADO.NET dataset.

I wrote an article in CoDe a few years ago that might help.

http://www.code-magazine.com/Article.aspx?quickid=0707051

If you click on the printer friendly link, you'll get the entire article in one long window.


Of particular interest...

- Tip #6 shows how to convert a LINQ result set (anonymous type) back to an ADO.NET datatable
- Tip #9 shows how to query an ADO.NET data table and use a GROUP and SUM