You need the latest version of Flash 10.1 installed for the flash radio control to work.
You can check which version is installed into your browser here
http://www.adobe.com/software/flash/about/You can get the latest version of flash here
http://get.adobe.com/flashplayer/By default Unreal Media Server uses port 5119. That may be your audio issue.
The javascript and flash should work in IE6, but its not recommended.
If your using RCFserver the port for the radio control should be 9034 (unless you modified it). Port 843 is used for security authorization by the Flash Player; you do not connect it it.