Multiple networks in one home?

I just picked up an airport extreme to replace my trusty netgear router so I can use it for NAS and printing over a WEP protected network. However, I would like to offer any guests that wander into our house the opportunity to freely hook up to some unprotected wifi via my old netgear router. If I plug the netgear into one of the ethernet ports on the airport extreme and leave it unprotected would they still have access to my NAS and printer? (I don't want them to, just internet) or would it be a separate "network"?

 

Ah, I'm not sure on that note. It was an ebay find and is in transit atm.