What does one have to do to be allowed to attend just to watch however?
NFA Day is offered at no-cost to those who don't currently have any Class 3 "toys" (machineguns, suppressors, SBRs, etc), for the purpose of educating them on NFA laws and to give them experience with the various "toys".
There is no requirement that you bring ammo, like in your case if funds are tight, but you'd shoot a lot more if you could at least bring some 9mm or .22LR.
Unfortunately the attendees for this year have already been picked, but you can always sign up for NFA Day 2012. We usually make an announcement and start signups 90 days out from the event, sometime near the end of the Summer.
Maybe we'll see you next year!