Precisely what happened to me...I changed to XP..and DigiChat quit...but I'm not sure now if it was coincidental or not.
Java certainly wasn't installed and was required. I did get a copy of Java from Sun..Chat would load to the sign in page and that was it.
I've been using another machine with windows ME..and..it's not working either...so..there must be something wrong with DigiChat..
In short...I think DigiChat is more the problem than our software.