This should give you an idea just drop this onto a new form dont change the name from form1 and put 3 comboboxes on the form. Its really basic but should show you how to do it.
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
ComboBox1.Items.Add("Toyota"

ComboBox1.Items.Add("Ford"

ComboBox1.Items.Add("Nissan"
End Sub
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
Select Case ComboBox1.Text
Case Is = "Toyota"
ComboBox2.Items.Add("Tundra"

ComboBox2.Items.Add("Corolla"

ComboBox2.Items.Add("Camry"

Case Is = "Ford"
ComboBox2.Items.Add("F150"

ComboBox2.Items.Add("Mustang"

ComboBox2.Items.Add("MustangGT"

Case Is = "Nissan"
ComboBox2.Items.Add("PathFinder"

ComboBox2.Items.Add("B2200"

ComboBox2.Items.Add("Other Nissan Car"

End Select
End Sub
Private Sub ComboBox2_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox2.SelectedIndexChanged
Select Case ComboBox3.Text
Case Is = "Tundra"
ComboBox3.Items.Add("PowerLocks"

ComboBox3.Items.Add("Sun Roof"

ComboBox3.Items.Add("50 Cal Machine Gun"

Case Is = "Corrola"
ComboBox3.Items.Add("Wheels w/ spikes"

ComboBox3.Items.Add("Oil Slicks"

ComboBox3.Items.Add("20000 Year Warranty"

Case Is = "Camry"
ComboBox3.Items.Add("Alarm"

ComboBox3.Items.Add("Gold Trim Package"

ComboBox3.Items.Add("A/C"

Case Is = "F150"
ComboBox3.Items.Add("Tires"

ComboBox3.Items.Add("A Motor"

ComboBox3.Items.Add("Windows"

Case Is = "Mustang"
ComboBox3.Items.Add("Doors"

ComboBox3.Items.Add("Roll Cage.. but why???"

ComboBox3.Items.Add("Muddin Tires"

Case Is = "MustangGT"
ComboBox3.Items.Add("Low Pros"

ComboBox3.Items.Add("Spokes"

ComboBox3.Items.Add("Ubah System"

Case Is = "PathFinder"
ComboBox3.Items.Add("M&M's"

ComboBox3.Items.Add("Floor Mats"

ComboBox3.Items.Add("A Rear view mirror"

Case Is = "B2200"
ComboBox3.Items.Add("Seats"

ComboBox3.Items.Add("Air Bags"

ComboBox3.Items.Add("Side Air Bags"

Case Is = "Other Nissan Car"
ComboBox3.Items.Add("BackSeat Airbags"

ComboBox3.Items.Add("Roof Airbags"

ComboBox3.Items.Add("Airbags for the Airbags"

End Select
End Sub
Hope it helps, Matt