I am planning to create a small research web application, that will have a graphical data representation control as a main data layout mechanism. The following sketch shows a primitive layout for a part of a web page:

Since it will be a part of a web app displayed in browser, I want to have some logic that allows me to create, edit and render such “maps” or you can call it “hierarchical trees” into HTML markup to sent to the browser.
Maybe one of you knows a good and elegant way to create such visual elements in plain html.
If not – I am a .Net developer, so I can, as a last resort, reduce to using a silverlight to render such visuals, but than I will have a huge visitor loss on a first visit, since most of them, I suppose, won’t be willing to install Silverlight Plugin, just to get acquainted with my web site.
Anyways, a plain HTML generator for such visual trees, or a Silverlight analog will be great. Thanks for the tip in advance.
P.S. I need the element to be interactive, so generating a simple image on a server is not the solution.
The JavaScript vector engine Raphael is a great option.
But if you just want to render the map and display the result on your page, then I recommend GraphViz which takes in a description of your graph in a simple language and outputs the graph in a few different formats.