Question: I need a JavaScript library, or Flash as well, which allows to connect events to "click" over "arcs" in graphics.

I've implemented my graphic through the JS-Graphs library, but I can only intercept the "click" event on "nodes", not on "arcs".

Answer: 
If you're interesting in using Flex, you may also want to take a look at Josh' Tynjala's [Wires UI](http://joshblog.net/2008/11/10/open-source-flex-project-wires-ui-library/) library.
[WireIt](http://javascript.neyric.com/wireit/) might be similar to what you're looking for. However, they use the YUI library and Canvas, so YMMV.