Lee, I second Jeroen's comments. We had ACS at some point but we were frustrated by the limitations imposed by the application. We wanted the freedom to write custom scripts for whatever we needed (guest access was one of them) and basically just wanted more control. We switched to FreeRADIUS and we've been extremely happy with it since. I know this doesn't help your current situation, though.
Thanks, Hector Rios Louisiana State University
