What about saving your dataTable not within your Settings. You could make use of DataTable.WriteXml(). this would keep your settings much smaller and you can access them separately!
' save table
DataTable.WriteXml("yourFile.xml")
' load table
Dim newTable As New DataTable
newTable.ReadXml(fileName)
But if there is no other possibility this solution from SLaks will work too
' save table
Dim writer As New StringWriter()
table.WriteXml(writer)
My.MySettings.Default.TableXml = writer.ToString()
' load table
Dim reader As New StringReader(My.MySettings.Default.TableXml)
table.ReadXml(reader)