Kevin,

Any time you insert characters into an item with transform() you need to use @R in the format string.

? transform( "123456789", "@R 99999-9999" )

Note though that if your field already contains the - the transform will actually insert another -

>Why does this not work?
>
>The ZipZode field is C(10) and contains
> "12345-6789"
>
>I use
>
> cZipCode = TRANSFORM(Addresses.ZipCode, "99999-9999")
>
>And I get back:
>
> "12345-789"
>
>What am I doing wrong?