Ok, So, in the place you specified, you want to determine if the button had been clicked previously and if so, goto PROCEED:

Let's see if this works ...

Code:
Private Sub Command1_Click()
    Do
        ani = ani + 1
        If ani = 7 Then ani = 1
        box1.Picture = MyPic(ani)
        box2.Picture = MyPic(ani)
        box3.Picture = MyPic(ani)
        If Command1.Tag = "CLICKED" Then
            Command1.Tag = ""
            Goto PROCEED
        End If
    Loop

PROCEED:
    Randomize
    a1 = Int((6 * Rnd) + 1)
    a2 = Int((6 * Rnd) + 1)
    a3 = Int((6 * Rnd) + 1)
    box1.Picture = MyPic(a1)
    box2.Picture = MyPic(a2)
    box3.Picture = MyPic(a3)
    If Command1.Tag <> "CLICKED" Then
        Command1.Tag = "CLICKED"
    End If
End Sub