What hardware do I need for a large network?

I am trying to set up a wireless network for my fraternity, which will have around 70 devices connected. Right now we are running two WRT54G routers for the entire house, and you can probably guess that it isn't working out very well.

We're looking at installing a new network with a wireless access point for each floor plus one outside, for a total of 5. I've been looking at some Cisco business-line WAPs but want recommendations on specific models, as well as what additional hardware I'd need. A main concern is roaming, so that all the WAPs would be broadcasting the same network.

I'd greatly appreciate any suggestions for WAPs, routers, etc; anything you think we'd need.