Allora:
vai nelle proprietà del progetto su references.
Fai add e selezioni prima microsoft.dirextx e poi microsoft.directx.audiovideoplayback.
Poi vai sull'editor e scrivi:
imports microsoft.directx
imports microsoft.directx.audiovideoplayback

Dichiari la variabile per il file mp3

Dim audiom as audio

e in seguito:

Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
PlayMP3()
End Sub

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
PlayMP3()
End Sub

Private Sub PlayMP3()
audiom = New Audio("file.mp3")
audiom.Play()
Timer1.Interval = audiom.Duration * 1000
End Sub