We presently use ISA for our wired PC's. Setup with the ISA firewall clients.
To avoid toutching student's PC's we also have different setup.
For wireless users we have AP's connected to a box doing filtering & NAT
- leading to a L3 routing sw. with static routing to the internal servers network and DGW set to internet router.
I have not worked with ASA, but I think it can be done:
http://www.experts-exchange.com/Hardware/Networking_Hardware/Firewalls/Q_22703615.htmlHTH