You can download the .xap file here:
http://www.rocktelevision.com/streaming/ClientBin/RockPlayer.xap
The easiest way to open it is via Windows Explorer but you need to patch your registry with this code:
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT.xap]
"PerceivedType"="compressed"
"Content Type"="application/x-silverlight-app"
@="CompressedFolder"
[HKEY_CLASSES_ROOT.xap\CompressedFolder]
[HKEY_CLASSES_ROOT.xap\OpenWithProgids]
"CompressedFolder"=""
[HKEY_CLASSES_ROOT.xap\PersistentHandler]
@="{098f2470-bae0-11cd-b579-08002b30bfeb}"
It worked for me.