yeah, it's built into the bottom. it's not a gasket as much as it is an o-ring kinda setup. flip over the stock TB and you'll see that lil' blue rubber piece. that's the gasket.
jeremy, just make sure you don't re-thread the screws that hole the TB into the intake. it's platics, and won't take too well to being messed with a bunch of times.
why r u playing with your TB, anyway? if you need a new stock one or a ported one, let me know. i'll give you either pretty cheap.
Mike