Try something like this (you will need a Timer control on your form):
Code:
Option Explicit
Private Sub Form_Load()
Me.Move (Screen.Width - Me.Width) / 2, _
(Screen.Height - Me.Height) / 2
Timer1.Interval = 1 '1/1000 of a second
Timer1.Enabled = True
End Sub
Private Sub Timer1_Timer()
Static i As Long
'delay a bit
i = i + 1
If i > 100 Then
Me.Move Me.Left + 1, Me.Top - 1
If Me.Left + Me.Width > Screen.Width Or Me.Top <= 0 Then
Timer1.Enabled = False
Unload Me
End If
End If
End Sub
NOTE: I left you plenty of room for improvements.