I have got mpegable working, through DSS to SL video viewers. It is much easier to set up than MPEG4IP/mp4live, and does have constant bitrate streaming. Get mpegable at
http://www.mpegable.de/
Click on mpegable Broadcaster, Buy Now, download free demo.
After installing, it puts a mpegable Player icon on your desktop, but look in the ...\mpegable\Broadcaster folder and you will see the exe for the Broadcaster. make a shortcut for it on your desktop.
I have written up how I configured it to make streams that will run through DSS to SL, the document is at
http://home.pacbell.net/rosk/mpegable.txt
Happy reading! IM questions and suggestions to Fremont Cunningham.