It may be worth a small amount because of its relation to Windows Vista. The hyphen hurts it quite a bitm aking it less friendly and awkward to use. Maybe in the low $xx range.
IMO it's not worth a lot.
Let's break down the domain keywords: vista: well-known word with possible TM issues (although I don't think you should worry in this case) hyphen: hurts the name us: do you mean USA ? Do you mean 'vista' (MS) software ? 'us' does not really fit then because software is not supposed to be country-specific.
What did you have in mind when you regged the name ? Perhaps you had an idea and I am missing something.
The hyphen really hurts the value, in addition to it having no real meaning besides maybe Windows Vista users in the USA, and if that's what you meant it probably would've been better to use .us