We've now done a full release of Interactive C. However, we are hosting it on the botball.org domain until we figure out the proper policies for our source code release that would let us keep using Sourceforge. I've taken down all the beta releases from this page, as they are no longer valid.
Woohoo! We're now all sourceforgey. IC 5 Beta (at least, the windows build) will be up as soon as I figure out how to get files on this thing.