The Vista Pre release comes in 2 forms an all day affair that covers everything that isn't in Vista that was supposed to be and the night time one for OEM Builders.
Well at least that's how it ran over here in AU. If you are going to the OEM System Builders one even if you are not a System Builder you'll get a lot from it as you get the real Tech types there and none of the marketing people who spin things so far out of skew that you no longer know if you're coming or going.
They should have a couple of suppliers there who offer a discount for orders of Vista and some other product that is Vista Compatible but that's country dependant so I'm not exactly sure what you'll see there though the drinks and nibbles after the show was over where great here and they ran a Lucky Door Prize which I avoid like the plague as if you enter you end up with heaps of spam delivered to your In Box.
Actually I saw very few of those that where there for the XP release at the Vista show and lots of new faces all of who think that they are going to get rich overnight and retire in a few months. It's a nice dream but somewhat short on reality though if you truly believe the M$ Spin Doctors if you are not retiring within 6 months you never can make a Buck. :D
Enjoy it anyway. :)
Col