From Christa Carpentiere:

The Knowledge Base is your friend

For about the umpteenth time, I've seen a newsgroup question on how to merge data from two or more DataTables responded to with a link to HOW TO: Implement a DataSet JOIN helper class in Visual C# .NET. This is just one in a series of KB articles on a DataSetHelper class that can be used to address common data merging and filtering questions. They can be handy - if you want to see what's available, just go to http://support.microsoft.com and search on "datasethelper".

Wow!  I knew that there where How To articles in the KBase, but I didn't know the depth of this subject. I wonder how much “gold” is in there...