practical question on planning new application: use flash, applet or SVG?

Hello. Recently we are starting a new project developing a simple
web-based workflow editor. 

In this web application users will use use drag-and-drop to create a
workflow chart within the browser. Requested feature:

     1. possible to print the chart using browser;
     2. possible to store workflow chart made by user on the server.
        e.g. the user edit a workflow, and save it. Later when he comes
        back to the website he can go on work on the workflow chart he
        yesterday saved;
     3. possible to export the workflow chart in any vector image format
        (can be done on server-side)
     4. application should run reasonably fast on Firefox on recent
        years hardware

Ideas we have now includes: 
     1. use html with javascript (will have difficulty drawing pointers
        and lines);
     2. Active Script with Flash
     3. javascript + SVG
     4. Java applet
     5. write an ActiveX control

We need to decide which technology to use mostly by estimate effort we
need to develop and maintain. Because at this moment we don't have
developer familiar with active script, Java and ActiveX, the developers
are all very familiar with javascript, thus SVG+Javascript looks like
the best solution for us. But I wish to ask the mailing list first in
order to have a rough idea of how difficult it is to develop such
application with SVG + Javascript. e.g. is it possible to write
drag-and-drop application with SVG + Javascript? Would the application
be too slow? Is there limitation in SVG or firefox support of SVG that
can make such application difficult to make?

I also couldn't find a fast-and-complex example of SVG application
similar to our project. If I can find such an example, it's easier to
gain confidence over this technology and firefox's support of it. Do you
happen to know such application?

Thank you very much in advanced.