Argh. What was so easy before isn't with ADO.NET & Windows'Forms. I'm trying to validate a simple textbox to ensure that it contains either an empty string or a nine digit number. Unfortunately when I'm changing from a valid numeric of any length to an empty string, the bound textbox is reverting back to that numeric value (which means that's what the DataSet is doing) when I try to go to the empty string. If there's a null in the database initially, that translates to an empty string, but not vice versa.

Anyhow, here's the answer:

Me.dsTemp.Tables(0).Rows("T_NAMESSN1") = DBNull.Value

Thanks to this link for getting me that last inch with DBNull.Value. Note that is a module-level CurrencyManager, which is needed to keep track of all where your GUI's pointing to in your DataSet.