Need simple wireless network management tool

Hello,

I am a person who is responsible for system administration in medium size broker's company (approx. 80 employees)

We have a lot of workers and visitors with Wi-Fi notebooks who want to surf internet it all over the campus.
Currently we have something like a dozen of Access Points (several conference rooms, trading room, lobby etc.)

that were configured separately. We have separate network for those APs because I'm afraid of intruders equipped with wi-fi sniffers who can penetrate into our LAN.

One more thing that make life difficult is the fact we had to configure WEP with the same key-phrase so users can surf via any one of our AP's.
What I'd like to know - is there some kind of simple software that can help me to manage the wireless network easily, including managing access for limited time visitors.

Also I'd like to know who is currently connected, how many users surf via wireless etc. The program must be simple to install and use, since this is only a part of my duties and I don't want to waste my time dealing with over-sophisticated network management tools (that cost tons of money).

Thanks,

Evgenek Klein,
MNGD