I have reached a major breakthrought today with that research. Basically, I can obtain a natif Excel spreadsheet from a dataset without any need of using a 3rd party tool, nor this Jet Engine, nor any fancy XML string that have to be manipulated. Based on some samples I found here and there, I put them all together in something that is working:

Imports System.IO
Imports System.Xml
Imports System.Xml.Xsl

Namespace Framework

    Public Class Export

        Public oApp As Framework.App

        ' Export a dataset into an Excel spreadsheet
        ' expO1 DataSet
        ' expC1 Full path of the file to save
        ' expC2 Full path of the transformation stylesheet
        Public Function ExportToExcel(ByVal toDataSet As DataSet, ByVal tcFile As String, _
         ByVal tcTransformationStyleSheet As String) As Boolean

            ' Read the dataset in a XmlDataDocument
            Dim loXmlDataDoc As XmlDataDocument = New XmlDataDocument(toDataSet)

            Dim loXslCompiledTransform As Xsl.XslCompiledTransform = New Xsl.XslCompiledTransform

            ' Get the Excel stylesheet into memory
            Dim loMemorySteam As New FileStream(tcTransformationStyleSheet, FileMode.Open, FileAccess.Read)

            Dim loXmlTextReader As XmlTextReader = New XmlTextReader(loMemorySteam)
            loXslCompiledTransform.Load(loXmlTextReader, Nothing, Nothing)
            Dim loStringWriter As New StringWriter()
            loXslCompiledTransform.Transform(loXmlDataDoc, Nothing, loStringWriter)

            ' Try to save the file
            If Not oApp.CreateFile(loStringWriter.ToString(), tcFile) Then
                Return False
            End If

            Return True
        End Function

    End Class

End Namespace

A big thanks to all who provided help on this topic.