Using Excel type formulae in VBA Forms

Okay I've tried my best to fix this all afternoon. My grasp of VBA is fairly basic at the moment but heres the problem:
I have a user form with 8 textboxes that take numeric values 0-10. There is then a 9th textbox which should show the sum of these 8 other textboxes, but I cant seem to get it to work. I know this would be easier in excel itself (using SUM(C1:C6) etc....), but I need it to be shown on the form.
Heres the code which doesn't work! ::

Dim Arr(8)

Arr(1) = TextBox1.Value
Arr(2) = TextBox2.Value
Arr(3) = TextBox3.Value
Arr(4) = TextBox4.Value
Arr(5) = TextBox5.Value
Arr(6) = TextBox6.Value
Arr(7) = TextBox7.Value
Arr(8) = TextBox8.Value

TextBox9.Value = xlSum = Arr(8)

I'm lost! Help would be most grateful.

[vba]

TextBox9.Value = Application.Sum(Arr)
[/vba]