I do not think you can use any other viewer for this purpose as the IP/TV Viewer is designed for Interactive sessions. Nevertheless there is nothing to lose trying though! :-)
Depends on several things...
1. If it's just a video/audio stream
2. How it's encoded
If you are just streaming audi/video and you are using MPEG1 you can use quicktime. If you are using a Mac, you can also download the MacTV client from www.iwitnesstv.com . It does support the question manager too.
Using just quicktime (on windows or the Mac) you can open URL and type in the rtsp://URL to the file you want. It may take some trial and error to get the file right.
Quicktime only supports MPEG1 by default, and though you can buy the MPEG2 encoder/decoder for QT it still doesn't support MPEG2 over RTSP as I understand it (though I haven't tested it one way or the other)
The streams are "MBONE compliant;" any viewer that can decode streaming MBONE video should be able to catch the Cisco multicasts (and vice-versa, the Cisco client can catch any MBONE-style multicasts).
For example, VBrick video is viewable on the Cisco client (or at least used to be, it's been a while), and the VBrick client can see the Cisco multicasts.