Screencast Video Stream
To live stream your desktop, you will want to get two pieces of software:

Software to capture your desktop as a stream and redirect:

1) CamTwist - http://camtwiststudio.com/download/ - does desktop live capture and turns it into a video stream that is compatible for "webcam" input applications. I've used this to live stream my desktop to ustream.tv, Google Hangout, etc. (free)

AND

2) SoundFlower - https://code.google.com/p/soundflower/ - Allows you to redirect the system sound output so that it can be routed as an input for your stream (free)

Software to publish from your desktop:

1) EvoCam - http://www.evological.com/evocam.html - does a local http streaming server to serve your "webcam" stream out to the local area network. ( $30 )

OR

2) VLC - http://www.videolan.org/vlc/streaming.html - VideoLAN streaming component of VLC to livestream your "webcam" produced from your camtwist/soundflower combo.  (free)

Can post more details, if this solution path works for you.

Edit: Note, a few test runs of VLC to export a stream crashes on my Mac. Looks like recent VLC builds support streaming the desktop, which is cool. With soundflower, you can also redirect the system output as well as the mic so that output from the apps and programs are livestreamed as well... provided your copy of VLC is running stably. :)

EDIT:

CamTwist is 32bit. So you will need to download the 32bit version of VLC for Mac OS X:

http://get.videolan.org/vlc/2.0.6/macosx/vlc-2.0.6-intel32.dmg


Fire up CamTwist
Select Desktop (not Desktop+) by double clicking it. This will add it to the list.
Select "Save Setup", and give it a name. 
Go to [tools]->[Studio], which will pop up a new window showing a list of "sources", a preview pane, and a program pane. Your new stream probably shows up in "Program", which is the "live webcam" indicator. You can select another source via the buttons and it will show up in the "green preview" window. Hitting "cut" will cut over from preview to program.
Fire up your 32bit VLC
[file]->[open capture device]
Under Capture Device, choose CamTwist.
check the [streaming] radio box
Choose the streaming settings
Choose the [stream] radio button
Leave most of the options as default
Hit OK
Hit Open
This should start the stream.


On my box, my copy of VLC happens to crash at this point, but then again, my version of VLC (2.06 and 2.10) both seem to crash when I try to stream anything. So it might be a problem on my system.

But the above is how I get CamTwist setup and VLC to see CamTwist.