1. 24-port business class switch 
2. Server (eg. Windows Small Business Server) to manage login access from the PCs
3. Small business router
4. Wireless access point with access controlled by server in #2 via RADIUS.

That should give you enough flexibility for future expansion.

Thanks for your feedback.  The network problems with the old router are occasional inability to connect from a distance, printer going offline for no reason when many users are online, network occasionally unavailable when crowded.  We were thinking of a more modest upgrade to a Linksys WRT160N or 400N.  Would this help?  Thanks again for your assistance!

Home routers are never designed for such aggregate use; therefore I wouldn't go with Linksys WRT series.  The bare minimum in your case would be Cisco Small Business Router WRVS4400N (this unit was formally marketed under the Linksys brand name but was rolled up to Cisco). Ideally in your situation the recommendation should be separate router + wireless access point. However if cost is really, really tight, the WRS4400N is the one I will go with.

I would echo mtrump's recommendation for the Linksys WRVS4400N in a low budget business-type environment, as well as to avoid using 'home routers' for that many devices.  The home based routers would work for a little while, but would likely encounter some issues with the quantity of connections, and their lifespan would be much shorter than normal.

Robert Paradis
ConnectPro Online Support Expert

Thanks!  You have been extremely helpful and I can now recommend a solution to our problem!