Hey Hillel,
You asked how to get Jin running inside of eclipse.  (Useful for using the debugger.)  I managed to get this working.  Here's what I did.
First, I set the following project settings:
Second, I run the ant build script, which creates the Jin/build directory.  This is necessary as it puts all the resource sets that Jin needs into the proper directories.
Third, I go to the Run menu and select Debug.  And in the Debug config window that pops up, I set the following settings:
Lastly, I hit the "Debug" button, and off she goes.  Once you've got all the settings configured, in the future, it should start up without any further configuration needed.
In reply to:
Hi all,
I use JIN for a while, and I thought it might be nice to try and help
with JIN development.
I am very new to open source development (CVS and stuff), and my java
knowledge is also lacking, so try and bare with me ;-).
I downloaded the jin branch from CVS, and tried running jin by going to
the directory jin/src/free/jin and typing :
java JinMain
that resulted in : "Exception in thread "main"
java.lang.NoClassDefFoundError: JinMain"

I thus have two questions:
1. how should I run JIN from the cvs sources?
2. I would really like to integrate the project with Eclipse (V3.0). I
actually managed to connect to the CVS through eclipse, and downloaded
the sources, but I was unable to run the project from within eclipse.
this is probably due to the same problem I didn"t manage to run it
through the command line. So if anyone managed to run the project in
Eclipse, with or without CVS integration, I would also love to hear some
suggestions on that.

OS : Mandrake Linux 10.0
Java : JRE 1.4.2_04
Eclipse V3.0

btw, complements to Sasha and all other developers for the great software.