Thanks, it works fine now. For others who are interested, here's a sample 
code.

    Public Sub PrintFile(ByVal aFileName As String)
        Dim myProcess As Process

        myProcess .StartInfo.FileName = aFileName
        myProcess .StartInfo.Verb = "Print"
        myProcess .StartInfo.UseShellExecute = True
        myProcess .StartInfo.CreateNoWindow = True
        myProcess .Start()
    End Sub