Try using the "or" condition.
vb Code:
  1. Private Sub Form_Load()
  2.     'To stop yourself from dividing by zero.
  3.     If Val(Text1.Text) And Val(Text2.Text) = 0 or  If Val(Text1.Text) And Val(Text2.Text) <> 0 Then
  4.     cmdDivide.Enabled = False
  5.     else
  6.     cmdDivide.Enabled = True
  7.     End If
  8. End Sub

I haven't tested the code but it should work.