One of the overloads for iTextSharp.text.Image.GetInstance()takes System.Drawing.Image, so convert your PNG resource to this type, and then use this overload. Something like that:
Dim test As System.Drawing.Image = System.Drawing.Image.FromHbitmap(My.Resources.MyImage.GetHbitmap())
Dim logo As iTextSharp.text.Image = iTextSharp.text.Image.GetInstance(test, System.Drawing.Imaging.ImageFormat.Png)