Most cards with TV out use, rely on the overlay window used by whichever player. Vegas however does not provide an ovelay window in preview, so alas, the answer is no - supposed to use your firewire out to a digital/analog convertor (often just the DV camera), and feed that to a TV monitor.

You might be able to find something or some way to just duplicate an area of your PC monitor's screen on a TV monitor - Matrox used to have such a setup - & that should work.