It sounds like they told you two truths that didn't add up. It is possible that the current servers don't support un-authenticated AirPort clients (on iBooks, anyway) because they are using something like a Microsoft NT network. Without a logon script (and the proper tools on the platform-that's your Mac-you can't log into the server and get access to the network. It is also possible that the Cicso access points (which may be fully 802.11b compliant or not-Cisco builds a lot of different boxes) may allow you to make a wireless connection without necessarily allowing you to log into the network. They may further muddy the water by implementing Cisco's "LEAP" authentication, which could keep you from being able to make a wireless connection at all.
The best bet is to contact the head of IT and ask what the actual school policies are-are Mac's specifically not supported and why, how do you go about getting an authorized wireless account, what limitations are there on accounts, etc. <cynical>I'd email the head of IT with these questions so the drones behind the support counter don't make your request "go away" because they don't understand Macs and don't want to learn.</cynical>