My first attempt to do this screen sharing thing is by following this super complex tutorial. http://howto.diveintomark.org/remote-mac/
The tutorial by Mark Pilgrim comes with videos and links and nice background music and such – making it looks highly reliable for beginner like me. It sounds like a very secure procedure, with explanation about SSH, man-in-the-middle and many more. However, this tutorial miss one crucial aspect regarding setting up fixed domain, tcp-forwarding and those ip related stuff that might confuse 99% of world population. Not to mention his tutorial only shows configuration for home internet with a particular ISP. The mac that I use for example was located behind CMU’s firewall and some other obstruction, making his tutorial to be only for geeks.
I could not set up the screen sharing capability through his tutorial.

*swearing phase*
For some reason all the VNC client that I use, RealVNC, TightVNC, UltraVNC does not seems to work properly. The clients fails with message like: ”Server did not offer supported security type” (tightVNC), ”No matching security types” (realVNC), ”Incompatible Version” (UltraVNC).
Then I google this error message only to found out this very long tutorial on how to tweak Mac to accept screen sharing. The tutorial can be found in this forum:
http://forums.macrumors.com/showthread.php?t=380251
In short, the tutorial asks me to perform some kind of surgery to the mac machine which obviously I was not so keen of doing so.
*swearing phase*
Then Justin, one of my research mentor pointed out that for mac, there should be no additional set up other than setting up screen sharing. He suspects its a mac-windows uneasy relationship thing.
After few googling I stumble upon one of the forum post somewhere – I forgot from where but it basically said I need to set the password for screen sharing so that those windows based client can actually connect to the mac.
IT WORKS… wtf
Here is how.
Go to (top-left-apple)-> system preferences->sharing->tick screen sharing together with the users that can be allowed to screen share.
Click Computer Setting to set up the password for allowing screen share.

Port forward: 5900 tcp for screen sharing over Internet