The easiest and best way is to purchase one or more wireless routers.
Hardware is always to be preferred to software because of it's stability and
hard coded firewall.

And to expand on that a little more, if you're supporting 75 to 100 users,
don't skimp on the bandwidth or the equipment. I would suggest at the very
minimum one full T-1 line and a few higher end Cisco wireless access points.
The cheaper Linksys routers will not handle all that traffic well.

I am currently using Cisco Commercial router and APs. I am
running an old version of Cisco's BBSM and would like to move away from that and
looking for a Linux solution.

I use ddwrt on linksys routers for this. Has the ability to add in ads too.

Do you have as many users as the person listed below? Does it take a
performance hit when that many people hit it at once?